Wireless, Handheld Tissue Oximetry Device

ABSTRACT

A system includes an enclosure having a processor and a memory coupled to the processor. The enclosure includes a display coupled to the processor where the display is visible from an exterior of the enclosure; and a battery within the enclosure coupled to the processor and the display. The enclosure includes a probe tip coupled to an exterior of the enclosure. The probe tip includes first, second, and third sensor openings. A first distance between the first and second sensor openings is different than a second distance between the first and third sensor openings. The enclosure includes code stored in the memory where the code is executable by the processor, and includes code to receive first data associated with the first and second sensor openings, code to receive second data associated with the first and second sensor openings, and code to perform SRS using the first and the second data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/220,354, filed Jul. 26, 2016, issued as U.S. Pat. No.10,456,066 on Oct. 29, 2019, which is a divisional of U.S. patentapplication 13/965,156, filed Aug. 12, 2013, issued as U.S. Pat. No.9,398,870 on Jul. 26, 2016, which claims the benefit of U.S. patentapplication 61/682,146, filed Aug. 10, 2012. U.S. patent applicationSer. No. 13/965,156 is a continuation-in-part of U.S. patent applicationSer. Nos. 13/887,130, 13/887,152, 13/887,220, 13/887,213, and13/887,178, filed May 3, 2013, which claim the benefit of U.S. patentapplications 61/642,389, 61/642,393, 61/642,395, and 61/642,399, filedMay 3, 2012. These applications are incorporated by reference along withall other references cited in this application.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical systems that monitoroxygen levels in tissue. More specifically, the present inventionrelates to optical probes, such as compact, handheld oximeters, thatinclude sources and detectors on sensor heads of the optical probes.

Oximeters are medical devices used to measure oxygen saturation oftissue in humans and living things for various purposes. For example,oximeters are used for medical and diagnostic purposes in hospitals andother medical facilities (e.g., operating rooms for surgery, recoveryroom for patient monitoring, or ambulance or other mobile monitoringfor, e.g., hypoxia); sports and athletic purposes at a sports arena(e.g., professional athlete monitoring); personal or at-home monitoringof individuals (e.g., general health monitoring, or person training fora marathon); and veterinary purposes (e.g., animal monitoring).

In particular, assessing a patient's oxygen saturation, at both theregional and local level, is important as it is an indicator of thestate of the patient's health. Thus, oximeters are often used inclinical settings, such as during surgery and recovery, where it can besuspected that the patient's tissue oxygenation state is unstable. Forexample, during surgery, oximeters should be able to quickly deliveraccurate oxygen saturation measurements under a variety of non-idealconditions. While existing oximeters have been sufficient forpost-operative tissue monitoring where absolute accuracy is not criticaland trending data alone is sufficient, accuracy is, however, requiredduring surgery in which spot-checking can be used to determine whethertissue can remain viable or needs to be removed.

Pulse oximeters and tissue oximeters are two types of oximeters thatoperate on different principles. A pulse oximeter requires a pulse inorder to function. A pulse oximeter typically measures the absorbance oflight due to pulsing arterial blood. In contrast, a tissue oximeter doesnot require a pulse in order to function, and can be used to make oxygensaturation measurements of a tissue flap that has been disconnected froma blood supply.

Human tissue, as an example, includes a variety of light-absorbingmolecules. Such chromophores include oxygenated and deoxygenatedhemoglobins, melanin, water, lipid, and cytochrome. Oxygenated anddeoxygenated hemoglobins are the most dominant chromophores in tissuefor much of the visible and near-infrared spectral range. Lightabsorption differs significantly for oxygenated and deoxygenatedhemoglobins at certain wavelengths of light. Tissue oximeters canmeasure oxygen levels in human tissue by exploiting theselight-absorption differences.

Despite the success of existing oximeters, there is a continuing desireto improve oximeters by, for example, improving measurement accuracy;reducing measurement time; lowering cost; reducing size, weight, or formfactor; reducing power consumption; and for other reasons, and anycombination of these.

Therefore, there is a need for an improved tissue oximetry devices andmethods of making measurements using these devices.

BRIEF SUMMARY OF THE INVENTION

Embodiments relate to a compact, handheld, tissue oximetry device thatincludes light sources and light detectors. Device implementations areentirely self-contained, without any need to connect, via wires orwirelessly, to a separate system unit for making oxygen saturationmeasurements. The sources and detectors are arranged in a circulararrangement having various source-detector pair distances that allow forrobust calibration, self-correction, and spatially-resolved spectroscopyin a compact probe. Other source-detector arrangements are alsopossible.

In an implementation, the device is a tissue oximeter, which can measureoxygen saturation without requiring a pulse or heart beat. A tissueoximeter of the invention is applicable to many areas of medicine andsurgery including plastic surgery. The tissue oximeter can make oxygensaturation measurements of tissue where there is no pulse; such tissue,for example, may have been separated from the body (e.g., a flap) andwill be transplanted to another place in the body.

According to one embodiment, a tissue oximetry system includes anenclosure that includes a first printed circuit board, housed within theenclosure. The first printed circuit board includes a processor and amemory where the memory is coupled to the processor. The enclosureincludes a display, coupled to the processor where the display isvisible from an exterior side of the enclosure. The enclosure includes abattery, housed within the enclosure where the battery is coupled to theprocessor and the display. The enclosure includes a probe tip, coupledto an exterior side of the enclosure where the probe tip includes atleast a first sensor opening, a second sensor opening, and a thirdsensor opening. A first distance is between the first and second sensoropenings, and a second distance is between the first and third sensoropenings. The first distance is different from the second distance. Theenclosure includes executable code, stored in the memory. The executablecode is executable by the processor and includes a first code to receivefirst data associated with the first and second sensor openings of thefirst distance, a second code to receive second data associated with thefirst and second sensor openings of the second distance, and a thirdcode to perform spatially-resolved spectroscopy using the first andsecond data.

According to a specific embodiment, the first sensor opening comprises alight source and the second and the third sensor openings comprise lightdetectors. In an alternative embodiment, the first sensor openingcomprises a light detector and the second and the third sensor openingscomprise light sources.

According to another specific embodiment, the probe tip includes a firstlayer comprising a second printed circuit board comprising a first lightsource, and includes a second layer, below the first layer. The probetip further includes a third printed circuit board comprising a firstlight detector and a second light detector. A third layer of the probetip is between the first and second layer and includes a first lenspositioned below the first light source. A fourth layer of the probe tipis below the third layer and includes a waveguide positioned below thefirst lens. The third printed circuit board may include a first aperturepositioned below the first lens. The waveguide may include an opticalfiber.

According to another specific embodiment, the executable code includes afourth code to calculate an estimated oxygen saturation value based onthe first and second data; and a fifth code to cause the display to showthe estimated oxygen saturation value.

According to another specific embodiment, the spatially-resolvedspectroscopy is dependent on the first distance and the second distancebeing different.

According to another specific embodiment at least one of the first, thesecond, and the third sensor opening comprises a light source; and theprobe tip comprises a temperature sensing unit positioned adjacent tothe light source. The temperature sensor is configured to generatetemperature information that represents the temperature of the lightsource. The processor is configured to receive the temperatureinformation and adjust a duty cycle of an oscillating control signalsupplied to the light source to adjust the luminosity generated by thelight source based on the temperature information if the temperature ofthe light source changes.

According to another specific embodiment, the probe tip is rigidlyattached to the housing and includes a pressure sensor for sensingpressure of the probe tip on tissue. The enclosure can be ten inches inlength or less and can be five inches or less across any lateral axis ofthe enclosure.

According to another embodiment, a method includes enclosing in ahousing a first printed circuit board comprising a processor and amemory, wherein the memory is coupled to the processor. The methodincludes providing a display, coupled to the processor and the housing,wherein the display is visible from an exterior side of the housing. Themethod includes enclosing a battery within the housing where the batteryis coupled to the processor and the display. The method includes forminga structure of the housing to retain the probe tip. The probe tip iscoupled to an exterior side of the enclosure, and the probe tipcomprises at least a first sensor opening, a second sensor opening, anda third sensor opening. A first distance is between the first and secondsensor openings, and a second distance is between the first and thirdsensor openings. The first distance is different from the seconddistance. The method includes configuring the probe tip to receive firstdata associated with the first and the second sensor openings; andconfiguring the probe tip to receive second data associated with thefirst and the third sensor openings. The method includes configuring theprocessor to perform spatially-resolved spectroscopy using the first andthe second data to determine an oxygen saturation value.

According to a specific embodiment, the method includes providing alight source for the first sensor opening; and providing light detectorsfor the second and the third sensor openings comprise light detectors.According to one alternative embodiment, the method includes providing alight detector for the first sensor opening; and providing light sourcesfor the second and the third sensor openings.

According to another specific embodiment, the method includes providingin the probe tip: a first layer comprising a second printed circuitboard comprising a first light source; a second layer, below the firstlayer, comprising a third printed circuit board comprising a first lightdetector and a second light detector; a third layer, between the firstand second layer, comprising a first lens positioned below the firstlight source; and a fourth layer, below the third layer, comprising awaveguide positioned below the first lens. The method includes formingin the third printed circuit board a first aperture positioned to bebelow the first lens. The waveguide may include an optical fiber.

According to another specific embodiment, the method further includesconfiguring the processor to calculate an estimated oxygen saturationvalue based on the first and second data; and configuring the processorto cause the display to the estimated oxygen saturation value. Thespatially-resolved spectroscopy is dependent on the first distance andthe second distance being different.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a tissue oximetry deviceaccording to one embodiment, and shows a number of processing modulesthat can be included in the tissue oximetry device.

FIG. 2 is a simplified block diagram of a sensor subsystem of the tissueoximetry device according to one embodiment.

FIG. 3 is a simplified block diagram of the acquisition module of thetissue oximetry device according to one embodiment.

FIG. 4 is a simplified block diagram of the measurement module of thetissue oximetry device according to one embodiment.

FIG. 5 is a simplified block diagram of the power source of the tissueoximetry device according to one embodiment.

FIG. 6 is a simplified block diagram of the sensor subsystem, theacquisition module, the measurement module, and the power source andshows flows of information and power through and between these elements.

FIGS. 7A and 7B are two overall perspective views of the tissue oximetrydevice according to one embodiment.

FIG. 7C is a side view of the tissue oximetry device.

FIG. 7D is a view of the tissue oximetry device where the housing isshown as substantially transparent and where various elements positionedin the housing are shown.

FIGS. 7E, 7F, and 7G are further enlarged views of the tip portion ofthe housing and the sensor head.

FIG. 7H is an alternative view of the sensor head.

FIG. 7I is an end view of the tip portion of the housing.

FIG. 7J is a simplified top view of a disk shaped end of the housing.

FIG. 7K is a simplified image of the cage.

FIGS. 8A and 8B are images of the tissue oximetry device being held by ahand of a user for use.

FIG. 9A is a simplified end view of the bottom of the probe tipaccording to one embodiment.

FIG. 9B is a simplified end view of the bottom of the probe tipaccording to an alternative embodiment.

FIGS. 10A and 10B are a simplified perspective view and an explodedview, respectively, of the source-sensor assembly that composes at leasta portion of the sensor subsystem.

FIG. 10C is a simplified front of the source printed circuit board.

FIG. 10D is simplified front view the detector printed circuit board.

FIG. 11A is a cross-sectional view of the source-sensor assembly andshows light emitted from one of the lighting elements and passingthrough one of the lenses and one of the fiber optic cables.

FIG. 11B is a cross-sectional view of the source-sensor assemblyaccording to one alternative embodiment where the spacer plate and thefiber optic cables are elongated.

FIG. 12 is a high-level flow diagram of a method for calibrating eachsource-detector pair according to one embodiment.

FIG. 13 is a high-level flow diagram of a method for calibrating thelight detectors according to one embodiment.

FIG. 14 is a high-level flow diagram of a method for detecting anomaliesduring use of the tissue oximetry device according to one embodiment.

FIG. 15 is a high-level flow diagram of a method for calibrating theamount of light emitted by the light sources.

FIG. 16 is a simplified schematic of light generated by the lightingelements (e.g., eight LEDs) in one of the light sources.

FIG. 17 is an example graph of a reflectance curve, which can be for aspecific configuration of the light sources and the light detectors.

FIG. 18A is a high-level flow diagram of a method for determining theoptical properties of tissue.

FIG. 18B is a high-level flow diagram of a method for finding theparticular simulated reflectance curve that best fits the reflectancedata points in the fine grid according to one implementation.

FIG. 19 is a high-level flow diagram of another method for determiningthe optical properties of tissue by the tissue oximetry device.

FIG. 20 is a high-level flow diagram of a method for weightingreflectance data generated by select light detectors.

FIG. 21 shows back and front views of a force sensing resistor.

FIGS. 22A and 22B are simplified images of the display.

FIG. 23 is a high-level flow diagram of a method for measuring thepressure of the probe tip against tissue being probed.

FIG. 24 shows an embodiment of the probe tip where the probe tip 300includes at least a dispenser portion of a tissue marker.

FIG. 25 is a high-level flow diagram of a method for marking tissue toindicate ranges of oxygen saturation of the tissue.

DETAILED DESCRIPTION OF INVENTION

Spectroscopy has been used for noninvasive measurements of variousphysiological properties in animal and human subjects. Visible (e.g.,red light) and near-infrared spectroscopy is often utilized becausephysiological tissues have relatively low scattering in these spectralranges. Human tissues, for example, include numerous light-absorbingchromophores, such as oxygenated hemoglobin, deoxygenated hemoglobin,melanin, water, lipid, and cytochrome. The hemoglobins are the dominantchromophores in tissue for much of the visible and near-infraredspectral range and via light absorption, contribute to the color ofhuman tissues. In the visible and near-infrared range, oxygenated anddeoxygenated hemoglobins have significantly different absorptionfeatures. Accordingly, visible and near-infrared spectroscopy have beenapplied to exploit these different absorption features for measuringoxygen levels in physiological media, such as tissue hemoglobin oxygensaturation (sometimes referred to as oxygen saturation) and totalhemoglobin concentrations.

Various techniques have been developed for visible and near-infraredspectroscopy, such as time-resolved spectroscopy (TRS), frequency-domaintechniques such as phase modulation spectroscopy (PMS), and continuouswave spectroscopy (CWS). In a homogeneous and semi-infinite model ofphysiological media, both TRS and PMS have been used to obtain theabsorption coefficient and the reduced scattering coefficient of thephysiological medium by use of the photon diffusion approximation orMonte Carlo models. From the absorption coefficients at multiplewavelengths, concentrations of oxygenated and deoxygenated hemoglobinscan be determined and from these concentrations, the tissue oxygensaturation can be calculated.

CWS generally does not possess enough information to separate theeffects of scattering and absorption. Accordingly, concentrations ofoxygenated and deoxygenated hemoglobins cannot typically be isolatedfrom one another. CWS has typically been used to solve a modifiedBeer-Lambert equation that requires assumptions about tissue scatteringand two or more wavelengths are used ratiometrically to cancel outoptical path length, which would otherwise be required to solve theequation. CWS, in its commonly-used form, provides relative oxygensaturation only and cannot provide absolute oxygen saturation orconcentrations of oxygenated and deoxygenated hemoglobins.

Despite the capability of TRS and PMS of providing hemoglobinconcentrations and absolute oxygen saturation, one major drawback of TRSand PMS equipment is that the equipment is bulky and relativelyexpensive. Another major drawback is that both of these techniques havedifficulty measuring through relatively small volumes of tissue (i.e.,“local” measurement, within a few millimeters). These techniques aretypically used for “regional” measurements (minimum of 1 centimeter) dueto the small time changes or phase shifts associated with short transittimes through small volumes of tissue. In contrast, CWS equipment can bemanufactured at a relatively lower cost, but is typically limited in itsutility as described above unless enhancements are made by eitherincluding broadband spectral information or by including spatialinformation. While current probes based on CWS have proven sufficientfor post-operative tissue monitoring where speed of measurement is lesscritical and relative rather than where absolute saturation measurementsare of concern. However, currently available probes have been shown togive inaccurate saturation measurements when used intraoperatively dueto common CWS assumptions. Embodiments of the presently describedinvention provide improvements in tissue oximetry over known devices.

Spatially-resolved spectroscopy (SRS) is one type of visible andnear-infrared spectroscopy that allows tissue absorption to bedetermined independently from tissue scattering, thereby allowingabsolute measurements of chromophore concentrations, such as oxygenatedand deoxygenated hemoglobins. More specifically, an SRS instrument mayemit light into tissue through a light source and collect the diffuselyreflected light at two or more detectors positioned at differentdistances from the light source.

Alternatively, an SRS instrument may emit light from two or more lightsources positioned at different distances from one or more detectors.Scattering of light back to the detectors is caused by relative changesin index of refraction of the tissue and includes Mie scattering fromlarger structures such as mitochondria (the majority of tissuescattering is a result of mitochondria) and Rayleigh scattering fromsmaller structures such as intracellular vesicles. Absorption of lightis caused by interaction with the tissue's chromophores.

From the reflectance (i.e., the recovered light intensity), which isrecovered as a function of distance (e.g., multiple discrete distancesof light detectors) from the light source, an SRS instrument canquantify the absorption coefficient and the scattering coefficient ofthe tissue at a single wavelength.

Multiple wavelengths of light can then be used with SRS to determineoxygenated and deoxygenated hemoglobin concentrations and thereforeoxygen saturation within the volume of the tissue probed. Further, thewavelengths of the light source or light sources and the relativepositions of the light source(s) with respect to the detectors, allowtissue oximetry measurements to be made for a predetermined tissuedepth.

One field in which visible and near-infrared spectroscopy, such as SRS,is useful is in tissue flap surgery in which a tissue flap is moved fromone location on a patient to another location for reconstructivesurgery. Visible and near-infrared spectroscopy techniques can be usedto measure oxygen saturation in a tissue flap so that the viability ofthe tissue flap can be determined in surgery and after surgery.Intraoperative tissue flap oximetry probes that employ visible andnear-infrared SRS should be able to quickly deliver accurate oxygensaturation measurements under a variety of non-ideal conditions. U.S.patent application Ser. Nos. 13/887,130, 13/887,220, 13/887,213,13/887,178, and 13/887,152, filed May 3, 2013, describing tissueoximetry devices that can use spatially-resolved spectroscopy, areincorporated by reference.

Tissue Oximetry Device

Embodiments of the present invention relate to tissue oximetry devicesthat use SRS to provide concentrations of oxygenated hemoglobin anddeoxygenated hemoglobin from which the tissue oximetry devices candetermine the estimated oxygen saturation. Embodiments of the tissueoximetry devices are relatively compact providing for ease of handhelduse by a single user.

FIG. 1 is a simplified block diagram of a tissue oximetry device 100according to one embodiment, and shows a number of processing modulesthat can be included in the tissue oximetry device. Tissue oximetrydevice 100 is a handheld device configured for handheld use by a singleuser and uses SRS for determining absolute oxygen saturation of tissue.

In an implementation, the tissue oximetry device displays an absoluteoxygen saturation which is a percentage value from 0 to 100 (or 0 to 99for a 2-digit display). In other implementations, the tissue oximetrydevice displays a value or other indication representation of anabsolute oxygen saturation. This representative value can be anotherrange (e.g., 0 to 20 or 0 to 50), indicator lights (e.g., LED lights),bar graph or gauge, or other indictor that is representative of theabsolute oxygen saturation. The scale of this alternative display of theabsolute oxygen saturation can be linear, geometric, logarithmic, orother scale.

Further, in other implementations, the tissue oximetry device displaysan estimated oxygen saturation of tissue. This estimated value can bethe absolute oxygen saturation discussed above, or other estimate of theoxygen saturation. This estimated oxygen saturation can be anintermediate value, that is determined using the circuitry andtechniques described in this application, and the absolute oxygensaturation is calculated or generated from this estimated oxygensaturation value. Then the device calculates the estimated oxygensaturation value (not displayed) and the absolute oxygen saturation(displayed). And alternatively, an estimated oxygen saturation value canbe determined from the absolute oxygen saturation.

According to the embodiment shown in FIG. 1, tissue oximetry device 100includes a handheld device housing 105 (bold surrounding line in FIG.1), a sensor subsystem 110, and acquisition module 115, a measurementmodule 120 (sometimes also referred to as a computation module), adisplay 125 (e.g., an optionally backlit liquid crystal display screen),one or more input controls 130, and a power source 135. Handheld devicehousing 105 (“housing”) is configured to house one or more of the abovelisted elements. Specific example embodiments of housing 105 aredescribed below.

Sensor subsystem 110 and acquisition module 115 can be communicativelycoupled via a bus system, and acquisition module 115 and measurementmodule 120 may also be communicatively coupled via a bus system. Powersource 135 can be configured to provide DC power, modulated power, orboth to sensor subsystem 110, acquisition module 115, and measurementmodule 120.

Sensor subsystem 110 includes various optical elements for generatingand emitting light or radiation (visible, infrared, or both) into tissue140, and collecting light scattered or reflected back from the tissueinto the sensor subsystem. Sensor subsystem 110 may generate reflectancedata from the scattered light detected by the sensor subsystem andtransmit the reflectance data to acquisition module 115 forpreprocessing. Measurement module 120 can be configured to receive thepreprocessed reflectance data from acquisition module 115 to determinethe oxygen saturation for the tissue. Measurement module 120 can becommunicatively coupled to one or more of input controllers 130 and todisplay 125. Based on user input received from one of the inputcontrollers 130, tissue oximetry module 100 may determine the oxygensaturation for the tissue, and display a result for the oxygensaturation on display 125.

Sensor subsystem 110 is currently further described. FIG. 2 is asimplified block diagram of sensor subsystem 110 according to oneembodiment. Sensor subsystem 110 may include one or more of lightsources 150 (e.g., two light sources) where each light sources includesone or more of lighting elements 152 a-152 n (referred to collectivelyas lighting elements 152), such as one or more light emitting diodes(LEDs), one or more laser diodes, or the like. Sensor subsystem 110 mayadditionally include a first set of optical devices 155 (e.g., classicaloptical devices, such as lenses, fiber optic cables, or the like) thatcollects emitted light from each light source 150 and directs theemitted light onto tissue 140.

Sensor system 110 may also include one or more temperature sensors 160,such as one or more thermistors, configured to detected the temperatureof light sources 150. In one embodiment, temperature sensors 160 arerespectively associated with light sources 150 and are configured tomeasure the temperature of the light sources.

Temperature sensors 160 may transmit temperature information for lightsources 150 to one or more of sensor subsystem 110, acquisition module115, measurement module 120, which may use the temperature informationregulate a control signal (e.g., a time varying control signal) suppliedto the light sources where the control signal controls the luminosity ofthe light sources. For example, as the LEDs of one of the light sourcesheat up and cool down, the efficiency of the LEDs changes and hence theluminosity of the LEDs may change.

Sensor subsystem 110, acquisition module 115, or measurement module 120,or a combination of these elements, may change the control signalsupplied to the LEDs so that the LEDs provide a substantially constantluminosity. For example, if a control signal, such as a sine wave shapedcontrol signal, is supplied to the LEDs, sensor subsystem 110,acquisition module 115, or measurement module 120, or a combination ofthese elements, may alter a duty signal of the control signal so thatthe LEDs provide a substantially constant luminosity as the LEDs heat upor cool down.

In an alternative embodiment, a photodetector can be positioned insensor subsystem 110, such as in a probe tip (described below), fordetecting increases, decreases, and no change in the luminosity of thelight sources. One or more of sensor subsystem 110, acquisition module115, and measurement module 120 can be communicatively connected to thephoto detector for receiving photodetector information, where thephotodetector information includes information for the increase,decrease, or lack of change (e.g., no change). One or more of sensorsubsystem 110, acquisition module 115, and measurement module 120 mayuse the received photodetector information for controlling the lightsources so that the light sources generate substantially constant oruniform luminosity.

In a specific implementation, the luminosity emitted by lightingelements 152 can be changed by sensor subsystem 110, acquisition module115, measurement module 120, or a combination of these if thetemperature of lighting elements 152 changes by a threshold amountbetween two successive measurements of the temperature made bytemperatures sensors 160. Specifically, if the temperature change is atthe threshold or within the threshold, the luminosity of the lightingelements might not be changed (e.g., the duty signal of the time varyingcontrol signal is held constant). Alternatively, if the temperaturechange is greater than the threshold, then the luminosity of thelighting elements can be changed (e.g., the duty cycle of the timevarying control signal can be raised or lowered or otherwise altered,accordingly) to maintain a substantially constant luminosity.

Sensor subsystem 110 may further include a second set of optical device165 that collects the light reflected from tissue 140 and directs thislight to one or more light detectors 170 a-170 n (referred tocollectively as light detectors 170), such one or more of PIN diodes,one or more photoresistors, or the like. Each light detector 170 maygenerate reflection data based on detected light, which can be used byacquisition module 115, measurement module 115, or both for generatingan oxygen saturation measurement for tissue 140. Further details of thespatial distribution of lighting sources 150 and light detectors 170 aredescribed below where the spatial distribution allows for SRS to beperformed by tissue oximetry device 100.

Sensor subsystem 110 may also include a pressure sensor 175 that isconfigured to detect a pressure of a sensor head of the sensor subsystemagainst tissue 140. Pressure sensor 175 may include one or more of aforce sensing resistor, a load cell, or the like. Pressure sensor 175 ismentioned briefly here, and is described further below. It is noted thatselect embodiments of tissue oximetry device 100 include pressure sensor175, while other embodiments of the tissue oximetry device might notinclude the pressure sensor.

Acquisition module 115 is currently further described. FIG. 3 is asimplified block diagram of the acquisition module according to oneembodiment. Acquisition module 115 may include a drive circuit 180, areflectance data collector 185, a pressure data collector 190, and asignal acquisition processor 195. Various embodiments of acquisitionsubsystem 115 may include some or all of these elements in anycombination. Via signal acquisition processor 195, drive circuit 180, orboth, acquisition module 115 may provide the varying control signal tolight sources 150 for controlling the light emitted therefrom. Forexample, signal acquisition processor 195 may supply a waveform, such asa digital waveform to drive circuit 180. The digital waveform can be adigital form of the time varying control signal (e.g., sine wave shapedcontrol signal) described above.

A digital-to-analog converter (DAC) 180 a of drive circuit 180 receivesthe digital waveform and convert the digital waveform to an analog formof the control signal (i.e., analog sine wave control signal) andsupplies or outputs the analog form of the control signal to a currentdriver 180 b. Signal acquisition processor 195 also supplies or outputsa predefined current pattern and a digital drive level to the drivecircuit 180. Current driver 180 b receives the current patternsubstantially directly from signal acquisition process 195 and receivesan analog form of the drive level from a second DAC 180 c of drivecircuit 180. Current driver 180 can use the analog form of the controlsignal, the pattern, and the drive level to supply the control signal tolight source 150 where the current drive may use the pattern and thedrive level to condition the control signal prior to transfer to sensorsubsystem 105.

Signal acquisition processor 195, measurement module 120, or both can beconfigured to receive temperature information from temperature sensor160 and adjust one or more of the control signal, the pattern, and thedrive level to increase or decrease the duty cycle of the controlsignal, based on the temperature as described above. More specifically,signal acquisition processor 195 can be configured to receive thetemperature information from a thermistor or the like (included intemperature sensor 160) for controlling the above described adjustments.Sensor subsystem 110 may include a temperature-information conditioningmodule (not shown) that can be configured to receive the temperatureinformation (e.g., an analog signal) and condition the temperatureinformation for use by signal acquisition processor 195, measurementmodule 120, or both. The temperature-information conditioning module canfilter the analog signal for the temperature information, convert thetemperature information to digital, or perform other operations thereonto make the temperature information useable by one or both of signalacquisition processor 195 and measurement module 120.

Turning now to reflectance data collector 185, the reflectance datacollector can be configured to receive raw reflectance data generated bylight detectors 170 and process the raw reflectance data. Morespecifically, reflectance data collector 185 can be configured toreceive, accumulate, filter, digitize, and average raw reflectance data,which may thereafter be converted into corresponding physicalquantities, such as light intensity. Reflectance data collector 185 mayinclude a signal conditioner 185 a that receives the raw reflectancedata and may filter the raw reflectance data as necessary. An analog todigital converter (ADC) 185 b, with a sample and hold circuit, mayconvert the raw reflectance data to a digital signal, which can beaveraged and correlated with the light emitted from the sources bysignal acquisition processor 195 for further processing may measurementmodule 120.

Correlation may include correlating calibration information for eachlight detector 170 with each lighting elements 152. That is, calibrationinformation used by tissue oximetry device 100 may include calibrationinformation for each light detector calibrated to each light source. Theluminosity of each light source, the gain of each light detector, orboth can be adjusted based on the calibration information.Alternatively, reflectance data generated by each light detector can beadjusted based on the calibration information by acquisition module 115(e.g., signal acquisition processor 195), measurement module 120, orboth. Generation of the calibration information is described furtherbelow.

Signal acquisition processor 195 can also be configured to control thegain of light detectors 170 (e.g., pin diodes) via issuance of a gaincontrol signal to acquisition module 115, which may convert the gaincontrol signal from a digital signal to an analog signal via a DAC 85 c,which in-turn provides the gain control signal to signal conditioner 185a for further transmission to one or more light detectors 170. Signalacquisition processor 195 may include one or more logic controlcircuits, such as a field programmable gate array (FPGA), a programmablelogic device (PLD), gate array, application specific integrated circuit(ASIC), a processor, or the like for performing the above-describedprocesses.

Measurement module 120 is currently further described. FIG. 4 is asimplified block diagram of measurement module 120 according to oneembodiment. Measurement module 120 may include a control processor 200,such as a microcontroller, a microprocessor, control logic, or the like,or any combination of these circuit elements. Measurement module 120 mayalso include a memory device 205. Memory device 205 may include one ormore of a variety of memory types, such as a disk (e.g., a micro diskdrive), Flash, or the like, where the memory device can be configured tostore computer code instructions, data (e.g., calibration information),or both. The stored computer code instructions, data, or both can beused by control processor 200, signal acquisition processor 195, or bothfor performing one or more of the methods and calculations describedherein, such the various methods for determining the oxygen saturationfor tissue 140 from collected light. Determination of the oxygensaturation is described in further detail below in the section of theapplication titled Monte Carlo Simulation.

After an oxygen saturation value for the oxygen saturation iscalculated, for example, as an indexed value of a percentage of totalpossible oxygen saturation of tissue 140 or as normalized value, theoxygen saturation value can be displayed on display 125. Determinationand display of the oxygen saturation value can be a repeating process.For example, oxygen saturation of tissue 140 can be determined a numberof times per second, such as three times per second. Two or moremeasurements, such as three measurements, of the oxygen saturation valuecan be averaged by control processor 200 for display on display 125. Forexample, three measurements of the oxygen saturation can be made in onesecond and can be averaged.

This average oxygen saturation value may then displayed on display 125and the displayed oxygen saturation value can be updated on the displayonce per second (e.g., at one hertz). Generally, averaging oxygensaturation measurements over relatively long periods is not performed sothat oxygen saturation measurements are not averaged for differentlocations on tissue 140. For example, if a user moves tissue oximetrydevice 100 from one location on the tissue to another location on thetissue, which often takes a second or longer, an average of the oxygensaturation values for these different locations should generally not bedisplayed on the display. Generally limiting the averaging to oxygensaturation values to a one second time frame limits the averaging ofoxygen saturation values for more than one tissue location.

Power source 135 is currently further described. FIG. 5 is a simplifiedblock diagram of power source 135 according to one embodiment. Powersource 135 may include one or more batteries 220, a power switch 225, apower convertor 230, or the like. Power source 135 may supply DC power,modulated power, or both to one or more of sensor subsystem 110,acquisition module 115, measurement module 120, display 125, and inputcontrollers 130. Power source 135 may also be communicative coupled tomeasurement module 120 where the measurement module may control thepower module to supply power for various power operation modes of tissueoximetry device 100, such as power up operations, standby mode, and thelike.

Battery 220 can be a disposable battery or a rechargeable battery. As isknown in the art, disposable batteries are discarded after their storedcharge is expended. Some disposable battery chemistry technologies thatcan be used in power source 135 include alkaline, zinc carbon, lithiumair, zinc air, or silver oxide. The batteries may include four 1.5-voltbatteries (e.g., AAA, AA, or N size batteries) or two 3-volt batteries(e.g., CR2032, CR2016, CR123A, and others) that are electrically inseries so that power source 135 may provide up to 6 volts to the variouscomponents of tissue oximetry device 100.

The batteries have sufficient stored charge to provide for use of tissueoximetry device 100 for several hours. For example, the batteries can beconfigured to provide two or more hours of use of tissue oximetry device100. After use, the tissue oximetry device 100 or a disposable portionthereof can be discarded. In other implementations, the batteries arerechargeable and can be recharged multiple times after the stored chargeis expended. Some rechargeable battery chemistry technologies that canbe used in power source 135 include nickel cadmium (NiCd), nickel metalhydride (NiMH), lithium ion (Li-ion), and zinc air. The batteries can berecharged, for example, via an AC adapter with a cord that connects tothe tissue oximetry device. The circuitry in the tissue oximetry devicecan include a recharge circuit (not shown) for battery recharge.Batteries with rechargeable battery chemistry may sometimes be used asdisposable batteries, where the batteries are not recharged but aredisposed of after use. Tissue oximetry device 100 can use rechargeablebatteries if the tissue oximetry device or a portion thereof isconfigured for reuse.

Power switch 225 of power source 135 can be a user operable switch thatcan be configured to operate with measurement module 120 for power up,power down, entering a standby power mode of operation, coming out ofthe standby power mode of operation, and other functions. For example,if tissue oximetry device 100 is powered down, an activation of powerswitch 225 may cause tissue oximetry device 100 to execute a power upsequence under control of measurement module 120. If tissue oximetrydevice 100 is powered on, a relatively short activation (e.g., less thantwo seconds) of power switch 225 may the place tissue oximetry deviceinto the standby power mode for saving battery power. If tissue oximetrydevice 100 is in the standby power mode, a subsequent relatively shortactivation (e.g., less that two seconds) of power switch 225 may placetissue oximetry device in full power mode relatively quickly. If tissueoximetry device 100 is in full power mode or in standby power mode, arelatively long activation (e.g., two second or longer) of power switch225 may cause tissue oximetry device to power down.

Measurement module 120 may also cause tissue oximetry device 100 toenter the standby power mode or power down if one or more criteria aremet, such as the tissue oximetry device not having been active for oneor more given periods of time. For example, measurement module 120 mayput tissue oximetry device 100 into the standby power mode if the tissueoximetry device is not active for 20 seconds and may put the tissueoximetry device in power down mode if the tissue oximetry device is notactive for 5 minutes.

After power up, tissue oximetry device may perform a variety of selfchecks, such as calibrating the pressure of the pressure sensor,clearing error messages that can reside in one or more of sensorsubsystem 110, acquisition module 115, measurement module 120, and powersource 135.

Power converter 230 of power source 135 can be a DC-to-DC converterconfigured to convert the voltage output from battery 220 to a varietyof DC voltages that are used by sensor subsystem 110, acquisition module115, measurement module 120, display 125, and input controls 130. Forexample, power converter 230 can be configured to output 1.2 volts, 2.5volts, 3.3 volts, 5 volts, 6 volts, or the like. Power converter 230 canbe configured to output one or more of these voltages at a given time.

For some embodiments, sensor subsystem 110, acquisition module 115,measurement module 120, display 125, input controls 130, and powersource 135 are sometimes referred to as self-contained electroniccomponents in that these electronic components may make a tissueoximetry measurement and provide information for oxygen saturation oftissue without the need to communicate (wired or wirelessly) with otherdevices (e.g., devices external to the tissue oximetry device'shousing). As such, some of the embodiments of tissue oximetry device 100are referred to as being self-contained.

FIG. 6 is a simplified block diagram of sensor subsystem 110,acquisition module 115, measurement module 120, and power source 135 andshows flows of information and power through and between these elements.The solid lines between the functional and circuit blocks indicate theflow of analog signals. The dashed lines with the relatively long dashindicate the flow of digital signals. The dashed lines with therelatively short dash indicate the flow of power. The mixeddashed-dotted line indicates the flow of mixed signals.

FIGS. 7A and 7B are two overall perspective views of tissue oximetrydevice 100 according to one embodiment. FIG. 7C is a side view of tissueoximetry device 100, and FIG. 7D is a view of tissue oximetry device 100where housing 105 is shown as substantially transparent. In thetransparent view of housing 105 in FIG. 7D, the positions of elements inthe housing are shown according to one embodiment.

In the particular embodiment of tissue oximetry device 100 shown inFIGS. 7A-7D, housing 105 includes a top portion 105 a that includesdisplay 125. Housing 105 also includes a body portion 105 b and a tipportion 105 c, which forms a portion of a sensor head 250. Top portion105 a of housing 105 is configured to be positioned upward with a userholding body portion 105 b in their hand and with sensor head 250pressed against the tissue of a patient. Top portion 105 a may orientdisplay 125 to face toward a user's face while the user holds bodyportion 105 b with sensor head 250 held against the tissue.

Housing 105 can be relatively compact, for example housing may about 25centimeters or less in length from top portion 105 a to sensor head 250,can be less than 13 centimeters wide across any lateral axis. Housing105 can be formed from a variety of materials, such as plastic, nylon,metal, or a combination of these. Housing 105 may conform to therequirements of UL/IEC/CAN 60601-1 and related documents for fluid spillresistance. Tip portion 105 c can be submersible to a level sufficientfor liquid phantom calibration.

At least one of the input controls 130 can be positioned on housing 105on an underside of top portion 105 a, and can be a button. The at leastone input control on the underside of top portion 105 a can be a powerbutton configured for powering on, powering off, standby power modeentry, and standby power mode exit (describe above).

In the specific embodiment of tissue oximetry device 100 shown in FIG.7D, acquisition module 115 includes a printed circuit board 115 a with anumber of circuits disposed thereon, such as the circuits of theacquisition module described above. Acquisition module 115 can bepositioned substantially in body portion 105 b of housing 105, such asalong a front side of body portion 105 b. As further shown in theembodiment of tissue oximetry device 100 in FIG. 7D, measurement module120 includes a printed circuit board 120 a with a number of circuitsdisposed thereon, such as the circuits of the measurement moduledescribed above. Measurement module 120 can be positioned substantiallyin top portion 105 a of housing 105, such as along an underside ofdisplay 125. Acquisition module 115 and measurement module 120 can befastened to housing 105 via a variety of fasteners, such as screws,nuts, and bolts, or the like, or via a variety of adhesives, such asepoxy, super glue, plastic weld, or the like. It is noted that whileacquisition module 115 and measurement module 120 are shown as being inbody portion 105 b and top portion 105 a, respectively, the locations ofthe acquisition module and the measurement module can be switched inhousing 105, may both be in the body section or may both be in the topportion. Batteries 220 can be positioned in housing 105 along a backsideof the housing and may extend from top portion 105 a to body portion 105b.

According to a specific embodiment, tip portion 105 c of housing 105 canbe configured as an arm that rigidly extends from body portion 105 b torigidly hold sensor head 250 and a probe tip 300 relatively fixed withrespect to housing 105 during use. In other embodiment, probe tip 300may be flex coupled to housing 105 or housing 105 may include a flexiblemember that provide flex for probe tip 300 when the probe tip is placein contact with tissue. For example, body portion 105 b may beconfigured as a flexile arm or may include one or more spring typedevices that allows probe tip 300 and sensor head 250 to provide flexfor the probe tip. Sensor head 250 or probe tip 300 can also includevarious spring type devices to provide for such flex or spring typequality.

In an implementation, a sensor head can be flexibly coupled via a springhaving a spring constant (e.g., operating according to Hooke's Law). Theflexible member coupling the sensor head to the enclosure can bedeformed elastically, so that it returns to its original form afterbeing deformed. This flexible sensor head can help prevent a user fromexerting too much pressure against tissue which the user is attemptingto measure.

In some embodiments tip portion 105 c, portions of body portion 105 b,sensor head 250, probe tip 300, or a combination of these can bedetachable from tissue oximetry device 100 and can be replaceable. Forexample, tip portion 105 c and sensor head 250 can be configured for usewith a single patient and can be detached from tissue oximetry device100 after use with the patient. Thereafter, the tip portion and thesensor head can be replaced with a new sterile tip portion 105 c and anew sterile sensor head 250 for use with a different patient. Theremaining body portion 105 b, top portion 105 a, and the electronicdevices contained therein can be configured to be reused with differentpatients after tip portion 105 c and sensor head 250, for example, arereplaced.

FIGS. 7E, 7F, and 7G are further enlarged views of tip portion 105 c andsensor head 250 according to one embodiment. Specifically, FIGS. 7E, 7F,and 7G are an enlarged side view, an enlarged front view, and anenlarged perspective view, respectively, of the sensor head and the tipportion of the housing. Tip portion 105 c of housing 105 may have a diskshaped end 105 d with an aperture formed therein for receiving afastener 250 a to attach the disk shaped end to a cage 250 b of thesensor head. Cage 250 b can be configured to hold together variouscomponents of the sensor head. For example, the disk shaped end 105 d oftip portion 105 c can have a recess formed therein where the recess canbe shaped to receive a nut 250 f (see FIG. 7H) that attaches to fastener250 a for attaching top portion 105 c to cage 250 b. Specifically, FIG.7H is a simplified side view of sensor head 250, which is shown withouttip portion 105 c of housing 105 and without probe tip 300 so that nut250 f can be shown coupled to fastener 250 a for a further understandingof the coupling of tip portion 105 c to cage 250 b. Further explanationof the view of sensor head 250 that is shown in FIG. 7H is providedbelow.

FIG. 7I is an end view of the disk shaped end 105 d of tip portion 105 cand shows a recess formed therein where the recess is centered about thecentral aperture of the disk shaped end. As described briefly above, therecess may have a hexagonal shape as shown or may have other usefulshapes for receiving nut 250 f or other similar fasteners.

Sensor head 250 can be 1.25 centimeters to about 4 centimeters long andabout 0.7 centimeters to about 2 centimeters wide (e.g., about 1centimeter in a specific embodiment). Tip portion 105 c of housing 105may have a length of about 9 millimeters to about 20 millimeters (e.g.,about 12 millimeters in a one specific embodiment). The disk shaped end105 d of tip portion 105 c may have a diameter of about 8 millimeters toabout 12 millimeters (e.g., about 10.6 millimeters in a one specificembodiment).

Sensor head 250 may additionally include one or more spring washers 250d and 250 e where the first spring washer 250 d can be positioned underthe head of fastener 250 a and the second spring washer 250 can bepositioned inside of cage 250 b and inside a second recess of diskshaped end 105 d where the second recess is formed in the top of thedisk shaped end. FIG. 7J is a simplified top view of disk shaped end 105d of housing 105 and shows the second recess formed in the top of thedisk shaped end where the recess is centered about the aperture formedtherein. Sensor head 250 can include one or more additional washerspositioned between the spring washers 250 d and 250 e and the top ofcage 250 b.

Sensor head 250 may additionally include a spacer 250 c positionedbetween disk shaped end 105 d and probe tip 300. In some embodiments,spacer 250 c is pressure sensor 175 (e.g., a force sensing resistor, aload cell, or both) configured to detect the pressure of probe tip 300against tissue. Pressure on probe tip 300 can be transferred to thepressure sensor where the pressure is detected by the pressure sensorand information for the detected pressure can be transferred from thepressure sensor to acquisition module 115, measurement module 120, orboth for reporting this detected pressure to a user, such as on display125.

Pressure detection and pressure reporting is described further below. Itis noted here however that a preload force can be placed on the pressuresensor, for example if the pressure sensor includes a load cell, via theforce applied by fastener 250 a, nut 250 f, and spring washers 250 d and250 e to the pressure sensor. The preload force can be increased ordecreased by tightening or loosening fastener 250 a and nut 250 f Thepreload force can also be used for calibrating the pressure sensor. Inembodiment where the pressure sensor is a load cell, the load cell canbe about 3 millimeters to about 5 millimeters in height and about 8millimeters to about 11 millimeters (about 9.6 millimeters in a specificembodiment) in diameter. The load cell can include a button end 250 gconfigured to contact probe tip 300 for detecting transferred pressureof the probe tip against the tissue.

FIG. 7K is a simplified image of cage 250 b. Cage 250 b can be metal,resinated fiber (e.g., carbon fiber, boron fiber, or the like), plastic,or the like. Cage 250 a may include a body portion 250 h (e.g., threearms), a top disk 250 i, and a bottom disk 250 j, where the body portionlinks the top disk to the bottom disk. Top disk 250 i may have a topaperture formed therein where the top aperture is configured to receivefastener 250 a. Bottom disk 250 j may have a bottom aperture formedtherein where the bottom aperture is configured to accept an apertureplate 430 (see FIGS. 7F, 10A, and 10B) of probe tip 300. Bottom disk 250j can form a shoulder for other portions of probe tip 300, such asdetector printed circuit board (PCB) 410 of probe tip 300. Probe tip300, detector PCB 410, and aperture plate 430 are described furtherbelow. Cage 250 b can be about 11 millimeters to about 14 millimeterslong (e.g., about 13 millimeters long in a specific embodiment). Cage205 b can have a diameter at the bottom of about 7 millimeters to about9 millimeters (e.g., about 8 millimeters according to one embodiment).Cage 250 b can have a diameter of about 8 millimeters to about 11millimeters at the broadest part of the cage.

FIGS. 8A and 8B are images of tissue oximetry device 100 being held by ahand of a user for use. Specifically, FIGS. 8A and 8B show the user'shand holding the body portion 105 b of housing 105 for use. In onemethod of use, a user may hold body portion 105 b with a thumb on afront of the body portion and with one or more fingers wrapped aroundback and sides of the body portion. The mass of tissue oximetry device100 may thereby be substantially supported by the user's fingers wrappedaround body portion 105 b. While the user's hand is shown as holdingbody portion 105 b of housing 105, a user can alternatively hold topportion 105 a of the housing or a combination of top portion and bodyportion.

Probe Tip

FIG. 9A is a simplified end view of the bottom of probe tip 300according to one embodiment. In the embodiment shown in FIG. 9A, probetip 300 includes two light sources 150 a and 150 b and eight lightdetectors 170 a to 170 h. While the specific embodiment in FIG. 9 showsthat probe tip 300 includes two light sources and eight light detectors,various alternative embodiments of probe tip 300 may include more or fewlight sources and may include more or fewer light detectors. Forexample, in one alternative embodiment, probe tip 300 may include threelight sources as shown in FIG. 9B.

As described above, light sources 150 are configured to generate andemit light (e.g., red and near-infrared light) into tissue that tissueoximetry probe 100 is in contact with. The tissue reflects a portion ofthe light and each light detector 170 detects a portion of the lightthat is reflected. Each light detector 170 generates reflectance data(i.e., a response) for the portion of light received, and sensorsubsystem 110 in combination with measurement module 115 determines anoxygen saturation of the tissue based on the reflectance data.

Light sources 150 can be linearly positioned across probe tip 300 andlight detectors 170 can be arranged in an arc or a circle (i.e.,circular arrangement) on probe tip 300. More specifically, light sources150 can be arranged on a line (e.g., a diameter) that bisects a circleon which light detectors 170 can be arranged. Light sources 150 a and150 b can be spaced a distance D1 apart where D1 may range from about 3millimeters to about 10 millimeters.

In an embodiment where probe tip 300 includes a central light source 150c (see FIG. 9B), the central light source 150 c can be positioned at anapproximate midpoint between light sources 150 a and 150 b. The centrallight source 150 c can be substantially equidistantly (e.g., +/−10microns) from each light detector 170 where the distance between thecentral light source and each light detector is about 1.5 millimeters to5 millimeters. That is, the circle on which light detectors 170 arearranged may have a diameter of about 3 millimeters to about 10millimeters (e.g., 4 millimeters according to one specific embodiment).

This maximum distance between the light sources and the detectorssubstantially limits reflectance data to light that propagated withinthe top layer of tissue wherein little or no underlying subcutaneous fator muscular layers contributes to the reflectance data generated bylight detectors 170 from light reflected from tissue. Propagation depthincreases with increasing source-to-detector distance, with about 4-5millimeters generally being a sufficient upper limit to ensure fewdetected photons propagated in lower tissue layers.

While light detectors 170 are described as being arranged in an arc orcircle, probe tip 300 may have other configurations of light detectors,such as linear, square, rectangular, pseudo-random, or other arbitrarypattern.

As described briefly above, the specific embodiment of probe tip 300shown in FIGS. 9A and 9B includes eight light detectors 170 a, 170 b,170 c, 170 d, 170 e, 170 f, 170 g, and 170 h. In other specificembodiments, however, probe tip 300 may include two or more lightdetectors 170.

Light detectors 170 can be solid state detectors and can be mounted todetector printed circuit board 410. Further, light detectors 170 can becombined devices or discrete devices.

Acquisition module 115, measurement module 120, or both can beconfigured to control light sources 150 and light detectors 170 via aset of electrical traces that run through the one or more printedcircuit boards on which the light sources and the light detectors aremounted. The circular configuration of light detectors 170 and thelinear arrangement of light sources 155 allows for a relatively simplearrangement of the electrical traces in these printed circuit boards.For example, the electrical traces may radially extend outward fromlights sources 150 and light detectors 170 so that the electrical tracesdo not overlap in the one or more PCBs on which these devices aremounted, which allows for relatively even spacing between the electricaltraces and thereby provides for relatively low electrical crosstalkbetween the electrical traces. In some situations, relatively lowcrosstalk between the electrical traces lowers the signal-to-noise ratioof both the light sources 150 and the light detectors 170 as compared toelectrical traces that are alternatively arranged.

In a specific implementation, light detectors 170 are positioned withrespect to light sources 150 a and 150 b such that two or more (e.g.,fourteen) unique source-to-detector distances are created. With greaternumbers of source-to-detector distances, this can be used to obtaingreater accuracy, faster calibration, and redundancy (when duplicatesource-to-detector distances are provided). At least onesource-to-detectors distances is about 1.5 millimeters or less (e.g.,0.5 millimeters up to about 1.7 millimeters), and at least onesource-to-detectors distances is about 2.5 millimeters or greater (e.g.,1.5 millimeters up to about 3.2 millimeters).

For example, in one embodiment, a first source-to-detector distance isabout 1.5 millimeters or less. A second source-to-detector distance isabout 1.5 millimeters or less. A third source-to-detector distance isabout 2.5 millimeters or greater. A fourth source-to-detector distanceis about 2.5 millimeters or greater. There can be various numbers oflight sources and light detector arrangements to obtain these foursource-to-detector distances, such as one light source and four lightdetectors, two light sources and two light detectors, one light detectorand four light sources, or other arrangements and combinations.

For example, one embodiment includes at least two light sources and atleast two light detectors, where a maximum distance between a lightsource and a light detector is about 4 millimeters (or about 5millimeters), where at least one source-to-detector distance is about2.5 millimeters or greater, and where at least one source-to-detectordistances is about 1.5 millimeters or less.

When a greater number of light sources and light detectors are includedin the probe tip, greater numbers of source-to-detector distances areavailable. As discussed, these can be used to provide greater accuracy,faster calibration, or redundancy, or a combination or these. Thearrangement of the light sources and light detectors can be in acircular pattern, such as at points along the arc of a circle withradius of about 4 millimeters to about 5 millimeters. In animplementation, a tolerance of the positions of the light detector orthe light source on the arc is within 10 microns of the arc curve. Inother implementations, the tolerance is within about 0.25 millimeters.

The foregoing described source-to-detectors distances allow for thedetermination of the scattering coefficient and the absorptioncoefficient via SRS from the reflectance data, which is generated bylight detectors 170. Specifically, the reflectance data that isgenerated by light detectors 170, which have relatively smallsource-to-detector distances (e.g., 1.5 millimeters or closer), is afunction of the scattering coefficient of tissue and not the absorptioncoefficient. Further, the reflectance data that is generated by lightdetectors 170, which have relatively large source-to-detector distances(e.g., 2.5 millimeters or farther), is a function of the μeff (theinverse of the penetration depth), where μeff is a function of both thescattering coefficient and the absorption coefficient. With at least twolight detectors 170 positioned at 1.5 millimeters or closer to at leastone light source 150, and with at least two detectors positioned at 2.5millimeters or farther from at least one light source 150, thescattering coefficient and the absorption coefficient can beindependently determined.

According to one specific embodiment, sixteen unique source-to-detectordistances are provided. The sixteen unique source-to-detector distancescan be: 150 a-170 d=1.000 millimeter; 150 b-170 h=1.249 millimeters; 150a-170 e=1.500 millimeters; 150 b-170 a=1.744 millimeters; 150 a-170c=2.000 millimeters; 150 b-170 g=2.261 millimeters; 150 a-170 f=2.500millimeters; 150 b-170 b=2.712 millimeters; 150 a-170 b=2.940millimeters; 150 b-170 f=3.122 millimeters; 150 a-170 g=3.300millimeters; 150 b-170 c=3.464 millimeters; 150 a-170 a =3.600millimeters; 150 b-170 e=3.708 millimeters; 150 a-170 h=3.800millimeters; and 150 b-170 d=3.873 millimeters where these distances mayvary by about +/−10 microns.

In one alternative embodiment, at least two of the source-to-detectordistances are the same, such as the shortest source-to-detectordistances. For example, the shortest source-to-detector distance D2between light source 150 a and light detector 170 e, and the shortestsource-to-detector distance D3 between light source 150 b and lightdetector 170 a can be the same. It follows that the source-to-detectordistance D4 between light source 150 a and light detector 170 a, and thesource-to-detector distance D5 between light source 150 b and lightdetector 170 e may also be the same. The source-to-detector distances D4and D5 are the longest source-to-detector distances for light sources150 a and 150 b. The foregoing description is for an example embodiment.For example, other pairs of source-to-detector distances can be thesame, such as the next to shortest source-to-detector distances, and thenext to longest source-to-detector distances.

With the exception of the shortest source-to-detector distance and thelongest source-to-detector distance for light sources 150 a and 150 b,the source-to-detector distances for light sources 150 a and 150 b canbe unique. As described above, probe tip 300 may have fourteen uniquesource-to-detector distances that allow for fourteen reflectance datapoints to be collected by light detectors 170 a-170 h from light emittedfrom light sources 150 a and 150 b.

Furthermore, the source-to-detector distances for light sources 150 aand 150 b may also be selected such that increases in these distancesare substantially uniform. Thereby, a plot of source-to-detectordistance verses reflectance detected by light detectors 170 can providea reflectance curve where the data points are substantially evenlyspaced along the x-axis. These source-to-detector distances and theuniform increase thereof for light sources 150 a and 150 b reduce dataredundancy and can lead to the generation of relatively accuratereflectance curves.

FIGS. 10A and 10B are a simplified perspective view and an explodedview, respectively, of a source-sensor assembly 400 that composes atleast a portion of sensor subsystem 110 according to one specificembodiment. Source-sensor assembly 400 includes probe tip 300, which islocated and one end of the source-sensor assembly. Probe tip 300 can becomposed of portions of one or more components of the source-sensorassembly.

In one embodiment, source-sensor assembly 400 includes detector PCB 410and source PCB 415 that are configured to electrically couple probe tip300 to acquisition module 115. Light detectors 170 can be mounted ondetector PCB 410, and light sources 150 can be mounted on source PCB410. Detector PCB 410 may include a rigid portion 410 a (shown asgenerally round in FIGS. 10B) to which light detectors 170 are mounted,and may include a flexible portion 410 b that is configured to routeelectrical signal between the light detectors and acquisition module115. Source PCB 415 may similarly include a rigid portion 415 a (shownas generally round in FIGS. 10B) to which light source 150 are mounted,and may include a flexible portion 415 b that is configured to routeelectrical signal between light sources 150 and acquisition module 115.

The flexible portion 410 b of detector PCB 410 and flexible portion 415b of source PCB 415 are shown in FIGS. 7C and 7D in a flexedconfiguration with rigid portions 410 a and 415 a coupled to cage 250 aand connector ends electrically and physically coupled to PCB 115 a ofacquisition module 115. The connector ends of flexible portions 410 band 415 b can be one of a variety of connectors types that areconfigured to couple to PCB 115 a. In one implementation, theconnector's ends of flexible portions 410 b and 415 b may include zeroinsertion force (ZIF) connectors that connect to corresponding ZIFconnectors on PCB 115 a. The electrical connectors on flexible portions410 b and 415 b may have a pitch of about 0.5 millimeters and can be10-pin FH12 series HIROSE connectors. The part number of the HIROSEconnectors can be FH12-10S-0.5SH. The flexible portions 410 b ofdetector PCB 410 and 415 b of source PCB 115 may each be about 40millimeters to about 50 millimeters long (e.g., a bout 46 millimeters inone specific embodiment) and can be about 4 millimeters to about 6.5millimeters wide (e.g., about 5.5 millimeters in one specificembodiment).

In one implementation, light sources 150 a and 150 b are mounted (e.g.,soldered) on rigid portion 415 a of source PCB 415. For example, iflight source 150 a includes a number of LEDs, these LEDs can be mountedon rigid portion 415 a, and if light source 150 b includes a number ofLEDs, these LEDs may also be mounted on rigid portion 415 a.

In another implementation, light detectors 170 are mounted (e.g.,soldered) on rigid portion 410 a of detector PCB 410. For example, iflight detectors 170 are photodiodes, these photodiodes can be mounted onrigid portion 410 a. FIG. 10C is a simplified front view of source PCB415 and FIG. 10D is simplified front view of detector PCB 410. Whilesource-sensor assembly 400 is described as including two PCBs that havethe light sources and light detectors mounted on the two different PCBs,the light sources and light detectors can be mounted on a single PCB.

Two sets of lenses 510 and 515 can be positioned adjacent to lightsources 150 a and 150 b, respectively, to direct light emitted fromthese light sources forward. More specifically, each set of lenses 510and 515 may include one or more lenses to direct light emitted fromlight sources 150 a and 150 b forward. According to one specificembodiment, the set of lenses 510 includes a number of lenses thatequals the number of lighting elements 152 in light source 150 a, andthe set of lenses 515 includes a number of lenses equal to the number oflighting elements included in light source 150 b. Further, the lenses inthe set of lenses 510 respectively correspond to lighting elements 152in light source 150 a, and the lenses in the set of lenses 515respectively correspond to the lighting elements 152 in light source515. The lenses can be hemispherical or the like. According to analternative specific embodiment, a single lens directs the light fromlight source 150 a forward and another single lens directs the lightemitted from light source 150 b forward.

Source-sensor assembly 400 may include a lens plate 420 that holds thelenses in alignment for substantially optimal forward direction ofemitted light. Lens plate 420 can be coupled between an LED apertureplate 425 and a spacer plate 427 where the LED aperture plate and thespacer plate have apertures formed therein that are adjacent to theapertures in lens plate 420 for permitting light emitted from lightsources 150 a and 150 b to pass forward from probe tip 300.

Contact plate 430 can be coupled to the front of the rigid portion 410 aof detector PCB 410. Both the rigid portion 410 a of detector plate 410and contact plate 430 have apertures formed therein for further allowinglight emitted from light sources 150 a and 150 b to pass forward fromprobe tip 300. Contact plate 430 may also include a number of aperturesformed therein for allowing the light scattered back from the tissue topass to light detectors 170.

In one embodiment, source-sensor assembly 400 includes first and secondfiber optic cables 435 a and 435 b (generally fiber optic cables 435,sometimes referred to as waveguides) that are optically coupled,respectively, to light sources 150 a and 150 a via the sets of lenses510 and 515. The fiber optic cables can be multimode glass fiber cables.One type of fiber optic cables that can be included in source-sensorassembly 400 has an outside diameter of about 440 micrometers and a corediameter of 400 micrometers.

The first and second fiber optic cables 435 a and 435 b can bepositioned in one or more of the apertures formed in aperture plate 425,in the rigid portion 410 a of detector PCB 410, and in contact plate430. In one embodiment, the sets of lenses 510 and 515 are,respectively, configured to focus the light emitted from light sources150 a and 150 b into the first and second fiber optic cables 435 a and435 b. The first and second fiber optic cables 435 a and 435 b areconfigured to diffuse the light (sometimes referred to as mixing thelight) so that the light emerges from the fiber optic cables withsubstantially homogeneous intensity across the openings of the fiberoptic cables to thereby evenly illuminate the tissue. The first andsecond fiber optic cables 435 a and 435 b may each be about 1 millimeterto about 20 millimeters long and in one particular embodiment are about10 millimeters long. The diameter of the first and second fiber opticcables 435 a and 435 b can be a function of the length of the fiberoptic cables. For example, the length of each fiber optic cable can beten times the diameter of the fiber optic cable so that a relativelyhomogeneous intensity of light is emitted therefrom.

FIG. 11A is a cross-sectional view of source-sensor assembly 400 andshows light emitted from one of lighting elements 152 passing throughone of the lenses 510 and passing through one of the fiber optic cables435 for emission into tissue 140. The cross-sectional view shows themixing of the light in the fiber optic cable. The cross-sectional viewalso shows the stacked configuration of probe tip 300 according to oneembodiment. The thicknesses of the various elements stacked in probe tip300 may not be drawn to scale in FIG. 11A.

Referring again to FIG. 10B, source-sensor assembly 400 further includetemperature sensor 160 (e.g., first and second thermistors 160 a and 160b) and include an end cap 440 according to one embodiment. End cap 400can be configured to house the temperature sensor. For example, end cap440 may include one or more recesses (e.g., first and second trenches),one or more apertures, or the like formed therein for holdingtemperature sensor 160 (e.g., thermistors 160 a and 160 b) adjacent tosource PCB 415 to monitor the temperature of the light sources.Thermistors 160 a and 160 b can be relatively elongated devices wherelongitudinal axes of the thermistors substantially align withconfigurations (e.g., square, rectangular, or the like) of lightingelements 152 of light sources 150 a and 150 b on source PCB 152.

FIG. 11B is a cross-sectional view of source-sensor assembly 400according to one alternative embodiment where spacer plate 427 and fiberoptic cables 435 a and 435 b are relatively elongated compared to theembodiments of spacer plate 427 and fiber optic cables 435 a and 435 bshown in FIG. 11A. For example, spacer plate 427 and fiber optic cables435 a and 435 b shown in the embodiment of FIG. 11A can be about 1millimeters to about 2.5 millimeters in height, and can about 5millimeters to about 20 millimeters in height in the embodiment shown inFIG. 11B. Each of detector PCB 410, source PCB 415, lens plate 420,aperture plate 425, spacer plate 427, and contact plate 430 can range inthickness from about 0.5 millimeters to about 2 millimeters. Thediameters of each of the rigid portion 410 a of detector PCB 410, therigid portion 415 a of source PCB 415, lens plate 420, aperture plate425, and spacer plate 427 can range from about 4 millimeters to about 10millimeters, and the diameter of contact plate 430 can range in diameterfrom about 3 millimeters to about 8 millimeters.

FIG. 10C is a planar view of source PCB 415 and shows lighting elements152 arranged in square configuration in both light source 150 a and 150b. While lighting elements 152 are shown in FIG. 10C as being in arelatively square configuration, the lighting elements can be arrangedin alternative configurations, such as rectangular, circular, ovoid, orthe like.

FIG. 10C further shows the connector end of source PCB 415 and shows theelectrical contact pads 415 c of the connector end. The electricalcontact pads may form portions of electrical traces that run from theconnector end to electrical pads on which the lighting elements areelectrically connected. Some of the electrical contact pads 415 c can beground pads that connect to ground traces, ground pads, or both. Thegrounds are configured to provide a controlled electrical environment(e.g., 50-ohm resistance for the electrical traces) for the controlsignals that are transmitted through the electrical traces to the lightsources. Electrical contact pads 410 c, electrical traces, and groundingelements of detector PCB 410 can be similarly configured as shown inFIG. 10D. In one embodiment, the outer most contact pads and traces indetector PCB 410 and source PCB 415 are the grounds, and the centralcontact pads and traces are the signal pads and traces.

While light detectors 170 are shown as being configured to receive lightsubstantially directly from the tissue, in one alternative embodiment,the light detectors can be configured to receive the light from one ormore fiber optic cables that route the light to the light detectors.Further, while light sources 150 and light detectors 170 are describedand shown as being in probe tip 300, the light sources and the lightdetectors can be located within housing 105, such as within body portion105 b of the housing. In this configuration, light sources 150 and lightdetectors 170 can be optically coupled to probe tip 300 via one or morefiber optic cables.

Calibration of Sources and Detectors

FIG. 12 is a high-level flow diagram of a method for calibrating eachsource-detector pair according to one embodiment. The high-level flowdiagram represents one example embodiment. Steps can be added to,removed from, or combined in the high-level flow diagram withoutdeviating from the scope of the embodiment.

At 1200, probe tip 300 contacts a tissue phantom, which has homogeneousoptical properties. Light is emitted from one or more of the lightingelements 152, step 1205, into the tissue phantom and at least some ofthe light is reflected back by the tissue phantom. Each light detector170 receives a portion of the light reflected from the tissue phantom,step 1210, and each light detector generates reflectance data (i.e., aresponse) for the portion of reflected light received, step 1215. Thereflectance data for light detectors 170 may not match a reflectancecurve for the tissue phantom (i.e., can be offset from the reflectancecurve). If the reflectance data generated by light detectors 170 doesnot match the reflectance curve for the tissue phantom, the lightdetectors may have an intrinsic gain or loss, or the light sources mayhave more or less power than simulated. The reflectance data generatedcan be used by one or more of sensor subsystem 110, acquisition module115, and measurement module 120 to generate a set of calibrationfunctions so that the raw reflectance data matches the reflectance curvefor the tissue phantom, step 1220. Raw reflectance data includes thereflectance data generated and output by the light detectors prior tobeing utilized for determining the optical properties for the tissue andbefore being utilized for determining oxygen saturation for the tissue.

Steps 1200 to 1220 can be repeated for one or more tissue phantoms. Thecalibration function for each source-detector pair for each tissuephantom should generally be the same. However, if there is a deviationbetween the calibration functions for a given source-detector pair for anumber of tissue phantoms, then the factors within the calibrationfunction for the given source-detector can be averaged. Each of thecalibration functions generated (including averaged functions) is storedin memory device 205, step 1225.

Steps 1200 to 1225 can be repeated for each of the lighting element 152in each of the light sources 150 a and 150 b. If steps 1200 to 1225 arerepeated for each of lighting elements 152 in each of the light sources150 a and 150 b, for example, then a number of calibration functions canbe stored in memory device 205 for each light detector 170, and each ofthe stored calibration functions for each light detector is associatedwith one of the lighting elements 152. That is, each source-detectorpair has a calibration function specifically for the source-detectorpair.

For example, light detector 170 a may have a first calibration functionstored for light emitted from a first lighting element 152 in lightsource 150 a, a second calibration function for a second lightingelement 152 in light source 150 a, a third calibration function for athird lighting element 152 in light source 150 a, a fourth calibrationfunction for a fourth lighting element 152 in light source 150 a, andthe like if light source 150 a includes more lighting elements 152.Further, light detector 170 a may also have a fifth calibration functionstored for light emitted from a first lighting element 152 in lightsource 150 b, a second calibration function for a second lightingelement 152 in light source 150 b, a third calibration function for athird lighting element 152 in light source 150 b, a fourth calibrationfunction for a fourth lighting element 152 in light source 150 b, andthe like if light source 150 b includes more lighting elements 152.

Because a calibration function is stored for each source-detector pair,the calibration functions (e.g., eight calibration functions) for eachlight detector provide calibration not only for variations in the lightdetectors but also for variations in the lighting elements 152 of thelight sources 150. For example, the intrinsic gain or loss for a lightdetector should not vary when receiving light from lighting elements 152in light source 150 a or 150 b. If the calibration functions differ fora light detector when receiving reflected light for different lightingelements, the difference in the reflectance data for a given tissuephantom is attributable to differences in the intensity of light emittedby the lighting elements. The calibration functions can be applied toreflectance data that is generated by light detectors 170 when tissueoximetry device 100 is used for oxygen saturation measurement in realtissue, for example, so that any intrinsic gains or losses of the lightdetectors 170, and any difference in the intensity of light fromlighting elements 152, can be compensated for. Specifically, thecalibration functions are applied on a source-detector pair basis forthe raw reflectance data generated by the detectors.

As described briefly above, a central light source 150 c can besubstantially equidistant (e.g., +/−10 microns) from each of lightdetectors 170 such that the light detectors can be relatively easilycalibrated using homogeneous tissue phantoms. The term “homogeneity”used with respect to a tissue phantom refers to the optical propertiesof a tissue phantom being substantially constant throughout the volumeof the tissue phantom. For example, the absorption coefficient μ_(a) andthe reduced scattering coefficient μ_(s)′ of a tissue phantom can bereferred to as being homogeneous (i.e., substantially constant)throughout the tissue phantom. This is in contrast to real tissue, whichexhibits anisotropic optical properties stemming from the intrinsicalignment of collagen fibers and other biological factors as well as thespatial variances, which may stem from differing degrees of tissuecomponents and oxygen saturation.

FIG. 13 is a high-level flow diagram of a method for calibrating lightdetectors 170 according to one embodiment. The high-level flow diagramrepresents one example embodiment. Steps can be added to, removed from,or combined in the high-level flow diagram without deviating from thescope of the embodiment.

At 1300, probe tip 300 contacts a tissue phantom, which has homogeneousoptical properties. Light (e.g., near infrared light) is emitted fromcentral light source 120 c, step 1305, into the tissue phantom and atleast some of the light is reflected back by the tissue phantom. Eachlight detector 170 receives the light reflected from the tissue phantom,step 1210, and each light detector generates a response to the reflectedlight, step 1315. Each light detector 170 should receive the same amountof reflected light due to the homogeneity of the tissue phantom. Anydifferences between light detector responses can therefore be attributedto physical differences between the light detectors. For example, one ormore of the light detectors may have an intrinsic gain or an intrinsicloss.

The responses from light detectors 170 are used by one or more of sensorsubsystem 110, acquisition module 115, and measurement module 120 togenerate calibration functions for the light detectors, where thecalibration functions can be used by one or more of sensor subsystem110, acquisition module 115, and measurement module 120 to flatten theraw reflectance data (i.e., the responses) generated by the lightdetectors to a single value, step 1320. The calibration functions or theresponses, or both, used for generating the calibration functions can besaved, e.g., in memory device 205, step 1325. The calibration functionscan be applied to the raw reflectance data that are generated by lightdetectors 170 when tissue oximetry device 100 is used to measure oxygensaturation levels in real tissue so that any intrinsic gains or lossesof the light detectors can be compensated for.

FIG. 14 is a high-level flow diagram of a method for detecting anomaliesduring use of tissue oximetry device 100 according to one embodiment.The high-level flow diagram represents one example embodiment. Steps canbe added to, removed from, or combined in the high-level flow diagramwithout deviating from the scope of the embodiment.

Tissue oximetry device 100 may employ the method to detect anomaliessuch as significant, spatially congruous inhomogeneities in real tissue.Such an inhomogeneity can indicate the presence of a mole or type oftissue that does not contribute relevant information regarding theoxygenated hemoglobin and deoxygenated hemoglobin concentrations in atissue flap, for example. The inhomogeneity could also indicate thatpart of the probe has gone beyond the edge of a wound or is covered byblood.

At 1400, light (e.g., near infrared light) is emitted from central lightsource 120 c into tissue, and the light is reflected by the tissue intoone or more of light detectors 170, step 1405. Each light detector 170generates a detector response to the received light, step 1410. If oneor more detectors lose contact with the tissue, then these detectors maygenerate a detector response, but the detector response might not be tolight emitted from central light source 120 c. Tissue oximetry device100 may determine whether the difference in the light detected (i.e.,detector response) by at least one of the light detectors differs by athreshold amount compared to light detected by one or more of the otherlight detectors, step 1415.

If the detector responses to light emitted from central light source 120c differ between the light detectors by the threshold amount (i.e., to agreater degree than predicted by ordinary tissue anisotropy), then thedetector responses from the at least one light detector in the clearminority of detector responses (i.e., detector response differs by atleast the threshold amount) can be discarded, step 1420, and not used tocalculate oxygen hemoglobin and deoxygenated hemoglobin concentrations.The at least one light detector in the clear minority can be assumed tohave been positioned in contact with a mole, blood, or other or to havelost contact with the tissue.

According to one alternative, if the detector responses generated by asignificant number (e.g., four) of light detectors 170 differsignificantly (e.g., by the threshold amount) from one another but thereis no clear majority of detector responses, then one or both ofacquisition module 115 and measurement module 120 may disregard all ofthe detector responses and may indicate (e.g., on display 125) thataccurate oxygen saturation cannot be determined for that currentlyprobed region of tissue. The steps of the method can be repeatedsubstantially continuously as tissue oximetry device 100 measures oxygensaturation in tissue. It is noted that central light source 120 c mightnot otherwise be used for obtaining contributive data for a reflectancecurve used for determining oxygen saturation.

Self-Correction of Data During Oxygen Saturation Detection

FIG. 15 is a high-level flow diagram of a method for calibrating theamount of light emitted by light sources 150 a and 150 b during oxygensaturation measurements on tissue or with a tissue phantom. Thehigh-level flow diagram represents one example embodiment. Steps can beadded to, removed from, or combined in the high-level flow diagramwithout deviating from the scope of the embodiment.

As described above, the shortest source-to-detector distances D2 and D3can be intentionally matched for the two outer light sources 150 a and150 b and the longest source-to-detector distances D4 and D5 may alsointentionally be matched for these light sources. With the shortestsource-to-detector distances matched, when outer source 150 a emitslight, step 1500, of a given wavelength into tissue and light detector170 e detects this light reflected from the tissue, step 1505, and whenlight source 150 b emits light into the tissue, step 1510, and detector170 a detects this light reflected from the tissue, step 1515, thereflectance data generated by light detectors 170 a and 170 e, steps1520 and 1525, respectively, should substantially match. That is, theamount of light detected by light detectors 170 a and 170 e shouldsubstantially match.

Further, with the longest source-to-detector distances matched, whenouter source 150 a emits light of a given wavelength into tissue andlight detector 170 a detects this light reflected from the tissue, andwhen light source 150 b emits light into the tissue and detector 170 edetects this light reflected from the tissue, the reflectance datagenerated by light detectors 170 a and 170 e should also substantiallymatch. If these pairs of reflectance data do not match, then the sourcepower of light sources 150 a and 150 b and the amount of light emittedby these outer sources may also be mismatched.

According to one embodiment, the tissue oximetry device uses these pairsof reflectance data (if mismatched) generated by light detectors 170 aand 170 e to correct the reflectance data generated by all of thedetectors and to correct the oxygen saturation analysis performed by thedevice. More specifically, a calibration function, step 1530, for thereflectance data (due to a source power difference between light sources150 a and 150 b) can be determined from the difference between theabsolute reflectance detected by light detectors 170 a and 170 e. Thiscalibration function can be applied to the raw reflectance datagenerated by each light detector 170 to compensate for the difference inthe amount of light emitted by light sources 150 a and 150 b.Specifically, two sets of reflectance data points that are offset fromeach other can be brought onto a single reflectance curve by applyingthe generated function to the reflectance data generated by each lightdetector 170 thereby generating relatively more accurate oxygensaturation data.

Tissue oximetry device 100 may substantially continuously monitor andcompare the reflectance data generated by light detectors 170 a and 170e to determine whether differences in the amount of light emitted fromthe light sources 150 a and 150 b occurs. Using the differences (ifpresent), the reflectance data for each of detectors 170 can besubstantially continuously corrected by tissue oximetry device 100during oxygen saturation measurements. According to one alternativeembodiment, the calibration of light sources 150 a and 150 b isperformed once and the generated function is stored for later use whilemaking oxygen saturation measurements.

According to one alternative, additional or alternativesource-to-detector distances can be matched for generating a functionfor the reflectance data due to source power difference between lightsources 150 a and 150 b (i.e., calibrating light sources 150 a and 150b). That is, the shortest or longest source-to-detector distances (or acombination of these) are not required for calibrating light sources 150a and 150 b and for correcting the reflectance data. Furthermore, whileusing two or more pairs of matched source-to-detector distances mayincrease the reliability or accuracy of the source calibration, a singlematched pair of source-to-detector distances can be used for calibratinglight sources 150 a and 150 b.

If a single matched pair of source-to-detector distances (e.g., D2 andD3) is used to calibrate light sources 150 a and 150 b and forcorrecting the reflectance data, then the signal-to-noise ratio of thereflectance data can be relevant for selecting the particularsource-to-detector distance to match. If minimal to low noise ispresent, then matching the longest source-to-detector distances mayprovide the most robust source calibration. However, noise may increaseas the square root of the magnitude of a reflectance data measurement,and therefore can be significantly larger for longer source-to-detectordistances. In this case, matching the shortest or relatively shortsource-to-detector distances may provide a more robust calibration ofthe outer sources and the reflectance data.

According to another alternative embodiment, all of thesource-to-detector distances for light sources 150 a and 150 b, and thelight detectors 170 a-170 h are matched providing four matchedsource-to-detector distances. Matching four source-to-detector distancesfor light sources 150 a and 150 b allows for the generation of tworeflectance data sets for each outer source, which can be compared toverify accuracy of the reflection data. The geometrical incorporation offast and robust calibration, self-correction, and accurate datacollection and processing methods limits fluctuations and inaccuracyseen in saturation measurements made by the intra-operative probesconsidered to be prior art. The previously discussed calibration,self-correction, and other features can lead to fast, accurate tissueoximetry devices, which should be desirable to plastic surgeons involvedin implant-based breast reconstruction and others concerned withdetecting tissue regions in danger of necrosis in surgical environments.

Light Waveform

FIG. 16 is a simplified schematic of a control signal that can besupplied to lighting elements 152 (e.g., eight LEDs) in light sources150 a. Specifically, FIG. 16 represents the control signal and mayrepresent the intensity of the light generated by the lighting elementsin one of the light sources at a given time. The pattern of the controlsignal and of the light generation shown in FIG. 16 can be sequentiallyrepeated by the light sources. In one embodiment, one lighting element152 at any given time receives the control signal and generates andemits light based on receipt of the control signal. That is, thelighting elements in a light source may sequentially receive the controlsignal. For example, a first lighting element (e.g., LED1) in one of thelight sources can receive the control signal and generate and emitlight, then a second lighting element (e.g., LED2) in the light sourcecan generate and emit light, then a third lighting element (e.g., LED3)in the light source can receive the control signal and generate and emitlight, and so forth until an eighth lighting element (e.g., LED8)receives the control signal for generating and emitting light.

The control signal can be a time varying control signal, such as asinusoidal control signal, that sinusoidally modulates the intensity oflight generated by each lighting element. In one specific embodiment,the frequency of the control signal 2.5 kilohertz frequency.

The control signal is supplied to each lighting element for a given time(sometimes referred to herein as a frame) which may include a number ofcycles (e.g., 6 cycles) of the control signal. The control signal cancycle the lighting elements from zero light generation and emission to apeak light generation and emission. In one embodiment, the sinusoidalcontrol signal that is supplied to each of the lighting elements startsat zero (e.g., zero current and voltage) so that the ramp up of lightgenerated by a lighting elements starts at zero light generation andrises with the sinusoidal waveform.

In one embodiment, each of the light detectors 170 samples the lightreflected from tissue 140 at a given frequency, such as at 100 sampleper cycles (i.e., sampling can be at 250 kilohertz) of the controlsignal. In some embodiments, light detectors 170 do not sample lightreflected from tissue during the first cycle of a frame where thelighting elements can be warming up to a stable operating temperature,or acquisition module 115, measurement module 120 or both can ignorereflectance data generated for the first cycle. Other methods can alsobe used for disregarding the first cycle of light generation by thelighting elements.

After all of the lighting elements 152 in a light source 150 generateand emit light for a number of consecutive frames (e.g., eights framesfor eight LEDs), then none of the lighting elements in the light sourcecan generate and emit light for the time period of a frame (e.g., e.g.,6 cycles of the control signal). Thereafter, another of the lightsources can generate and emit light as described above. To brieflysummarize, as referred to herein, a cycle is one cycle of the controlsignal; a frame comprises multiple cycles (e.g., 6 cycles); a windowcomprises a sequence of frames (e.g., one frame for each LED and onedark frame); and a measurement uses multiple windows over which thereflectance data is generated and processed by measurement module 120.

According to one particular embodiment, the lighting elements 152 ofeach light source 150 a and 150 b are configured to generate and emitlight at wavelengths of 760 nanometers (e.g., +/−10 nanometers), 810nanometers (e.g., +/−10 nanometers), 845 nanometers (e.g., +/−20nanometers), and 895 nanometers (e.g., +/−10 nanometers). Lightingelements 152 can sequentially generate and emit light in the above order(e.g., 760 nanometers, 810 nanometers, 845 nanometers, and 895nanometers) for each of the light sources 150 a and 150 b. While thelight sources 150 a and 150 b are described herein as including fourlighting elements 152, alternative embodiments of light sources 150 aand 150 b include more or fewer lighting elements.

For example, according to an embodiment where each of the light sources150 a and 150 b include two lighting elements, these lighting elementsin each light source can generate and emit the wavelengths ofapproximately 760 nanometers (e.g., +/−10 nanometers), and 850nanometers (e.g., +/−20 nanometers). According to an embodiment whereeach light source 150 includes three lighting elements, the lightingelements can be configured to generate and emit wavelengths ofapproximately 760 nanometers (e.g., +/−10 nanometers), 810 nanometers(e.g., +/−10 nanometers), and 850 nanometers (e.g., +/−20 nanometers).According to another embodiment, where each light source 150 includesfour lighting elements, the lighting elements can be configured to emitwavelengths of approximately 760 nanometers (e.g., +/−10 nanometers),810 nanometers (e.g., +/−10 nanometers), 850 nanometers (e.g., +/−20nanometers), and 900 nanometers (e.g., +/−20 nanometers). Additionaland/or alternative wavelengths can be utilized by tissue oximetry device100.

Use of the described wavelengths by tissue oximetry device 100 tends todecrease the fraction of emitted light that can be absorbed by methyleneblue, gentian violet, and povidone-iodine (PVPI), and thereby increasesthe fraction of light that can be scattered or absorbed by intrinsictissue elements and generates accurate reflectance data. The dyes areoften used by in the operating room to mark tissue. Accurate reflectancedata is necessary in order to extract the optical properties of tissuefrom which the concentrations of oxygenated and deoxygenated hemoglobincan be derived.

For the foregoing described wavelengths, tissue scattering is relativelylow and light penetrates farther into tissue than shorter wavelengths.Further, the foregoing described wavelengths are on both sides of anoxygenated-deoxygenated hemoglobin spectral crossing point called anisosbestic point, which is 810 nanometers for hemoglobin. As such, whenone chromophore (e.g., oxygenated hemoglobin) has high absorption, theother chromophore (e.g., deoxygenated hemoglobin) then has lowabsorption and vice versa. The tissue oximetry device's utilization ofwavelengths surrounding the isosbestic point provides for relativelyimproved statistics for oxygen saturation determinations.

In at least one of the previous described embodiments, tissue oximetrydevice 100 utilizes a wavelength at approximately the isosbestic point,at 810 nanometers. At the isosbestic point the absorption of the 810nanometer wavelength for oxygenated hemoglobin and deoxygenatedhemoglobin are equivalent and therefore provides a stable referencepoint in the reflectance data generated by light detectors 170.Relatively longer wavelengths, such as the 900 nanometer wavelength ofat least one embodiment allows for distinguishing between the absorptioncurves for deoxygenated hemoglobin from the absorption curve formelanin.

Use of Wavelengths for Optical Probing.

Oxygenated and deoxygenated hemoglobin concentrations, from which oxygensaturation can be calculated, can be related to the absorptioncoefficient μa of a region of tissue for a given wavelength of light. Insome cases, a simple relationship is used for calculation where theabsorption coefficient is assumed to depend only on the concentrationsof oxygenated and deoxygenated hemoglobin. However, melanin and waterpresent in tissue can also absorb incident light so this simplerelationship can be insufficient for highly accurate concentrationcalculations, as absorption from water and melanin can be incorrectlyattributed to oxygenated or deoxygenated hemoglobin. A relationshipbetween the absorption coefficient and the concentrations of oxygenatedhemoglobin (HbO2), deoxygenated hemoglobin (Hb), water (H2O), andmelanin (mel) can be:

μ_(a)=2.303(ε_(HbO2)[HbO2]+ε_(Hb)[Hb]+ε_(H2O)[H2O]ε_(mel)[mel])

where ε_(species) denotes the molar absorptivity of a given species andbracketed quantities indicate concentration values.

The shape of a reflectance curve (generated by plotting the intensity ofdiffusely reflected or re-emitted light) can be analyzed to obtain theabsorption and scattering coefficients for a given region of tissue.There are four unknown concentrations (i.e., [HbO2], [Hb], [H2O], and[mel]) in the above relationship that correspond to the absorptioncoefficient. Once the absorption coefficient is determined for a givenwavelength, the relationship becomes an equation of four unknownvariables. However, since the concentrations of oxygenated anddeoxygenated hemoglobin, water, and melanin should not vary considerablyover the course of a probe measurement, probing the tissue with fourdifferent wavelength emitted by the wavelength sources can provide fourvalues for μa, which can be used to determine the four relevantconcentrations in the expression for μa. That is, a system of fourequations with four unknown variables can be solved, as is wellunderstood. From the determined concentrations of oxygenated hemoglobins[HbO2] and deoxygenated hemoglobins [Hb], the oxygen saturation oftissue can be determined.

According to the embodiment where three wavelengths are emitted by thewavelength sources, the contributions from water, melanin, and otherlight absorbers can be combined into a single term and expressed as:

μ_(a)=2.303(ε_(HbO2)[HbO2]+ε_(Hb)[Hb]+ε_(H2O,mel)[H2O, mel]).

If three absorption coefficients u_(a) are determined for the threewavelengths, then the three relevant concentrations for [HbO2], [Hb],and [H2O, mel]) can be determined, and the oxygen saturation can againbe determined from the determined concentrations of oxygenated anddeoxygenated hemoglobins. The absorption coefficients can be determinedfrom the reflectance data by a variety of methods, such as fitting thereflectance data to one or more predetermined reflectance curves, whereeach predetermined reflectance curve represents a unique absorptioncoefficient. The absorption coefficients may alternatively be determinedby vector multiplication with the net analyte signal, which is describedin U.S. Pat. No. 6,597,931, titled “System and Method for AbsoluteOxygen Saturation,” and is incorporated by reference.

Monte Carlo Simulation

According to a specific embodiment, memory device 205 stores a number ofMonte Carlo-simulated reflectance curves 600 (“simulated reflectancecurves”), which can be generated by a computer for subsequent storage inthe memory device. Each of the simulated reflectance curves 600represents a simulation of light (e.g., visible or near infrared light)emitted from one or more simulated light sources into simulated tissueand reflected from the simulated tissue into one or more simulateddetectors. Simulated reflectance curves 600 are for a specificconfiguration of simulated light sources and simulated detectors, suchas the configuration of lighting elements 152 in light sources 150 anddetectors 170 in probe tip 300. Therefore, simulated reflectance curves600 model light emitted from, and collected by, tissue oximetry device100.

Further, each of the simulated reflectance curves 600 represents aunique real tissue condition, such as specific tissue absorption andtissue scattering values that relate to particular concentrations oftissue chromophores and densities of tissue scatterers. The number ofsimulated reflectance curves stored in memory device 205 can berelatively large and can represent nearly all, if not all, practicalcombinations of optical properties and tissue properties that can bepresent in real tissue that is analyzed for viability by tissue oximetrydevice 100. While memory device 205 is described herein as storing MonteCarlo-simulated reflectance curves, memory device 205 may storesimulated reflectance curves generated by methods other than Monte Carlomethods, such as using the diffusion approximation.

FIG. 17 is an example graph of a reflectance curve, which can be for aspecific configuration of light sources 150 and light detectors 170,such as one of the configurations light sources and detectors of probetip 300, or the like. The horizontal axis of the graph represents thedistances between light sources 150 and light detectors 170 (i.e.,source-detector distances). If the distances between light sources 150and light detectors 170 are appropriately chosen, and the simulatedreflectance curve is a simulation for light sources 150 and lightdetectors 170, then the lateral spacings between the data points in thesimulated reflectance curve will be relatively uniform. Such relativelyuniform spacings can be seen in the simulated reflectance curve in FIG.17. The vertical axis of the graph represents the simulated reflectanceof light that reflects from tissue and is detected by light detectors170. As shown by the simulated reflectance curve, the reflectance thatreaches light detectors 170 varies with the distance between lightsources 150 and light detectors 170.

According to one implementation, memory device 205 stores a selectnumber of points for each of the simulated reflectance curves 600 andmight not store the entirety of the simulated reflectance curves. Thenumber of points stored for each of simulated reflectance curves 600 maymatch the number of source-detector pairs. For example, if probe tip 300includes two light sources 150 a and 150 b and includes eight lightdetectors 170 a-170 h, then tissue oximetry probe 100 includes sixteensource-detector pairs, and memory device 205 may thus store sixteenselect data points for each of the simulated reflectance curves, wherestored data points are for the specific source-detectors distances(i.e., distances between the light sources and the light detectors).

Thus, the simulated reflectance curve database stored in memory device205 can be sized 16 by 3 by 5850 where sixteen points are stored percurve for three different wavelengths that can be generated and emittedby each light source 150 and wherein there are a total of 5850 curvesspanning the optical property ranges. Alternatively, the simulatedreflectance curve database that is stored in memory device 205 can besized 16 by 4 by 5850, wherein sixteen points are stored per curve forfour different wavelengths that can be generated and emitted by eachlight source and wherein there are a total of 5850 curves spanning theoptical property ranges. The 5850 curves originate, for example, from amatrix of 39 absorption coefficients μ_(s)′ values and 150 absorptioncoefficient μ_(a) values. The μ_(s′) values can range from 5:5:24centimeter⁻¹ (μ_(s)′ depends on the value for g). The μ_(a) values canrange from 0.01:0.01:1.5 centimeter⁻¹. It will be understood that theabove described ranges are example ranges and the numbersource-detectors pairs, the number of wavelengths generated by eachlight source, and the number of simulated reflectance curves can besmaller or larger.

Tissue Analysis

FIG. 18A is a high-level flow diagram of a method for determining theoptical properties of tissue (e.g., real tissue) by tissue oximetrydevice 100 where the tissue oximetry device uses reflectance data andsimulated reflectance curves 600 to determine the optical properties.The optical properties may include the absorption coefficient μ_(a) andthe scattering coefficients μ_(s) of the tissue. A further method forconversion of the absorption coefficient μ_(a) and the scatteringcoefficients of the tissue μ_(s) to oxygen saturation values for tissueis described in further detail below. The high-level flow diagramrepresents one example embodiment. Steps can be added to, removed from,or combined in the high-level flow diagram without deviating from thescope of the embodiment.

At 1800, tissue oximetry device 100 emits light from one of the lightsources 150, such as light source 150 a into tissue. Probe tip 300 isgenerally in contact with the tissue when the light is emitted from thelight source. After the emitted light reflects from the tissue, lightdetectors 170 detect a portion of this light, step 1805, and generatereflectance data points for the tissue, step 1810. Steps 1800, 1805, and1810 can be repeated for multiple wavelengths of light and for one ormore other light sources, such as light source 150 b. The reflectancedata points for a single wavelength can include sixteen reflectance datapoints if, for example, probe tip 300 provides sixteen source-detectorsdistances. The reflectance data points are sometimes referred to as anN-vector of the reflectance data points.

At 1815, the reflectance data points (e.g., raw reflectance data points)are corrected for gain of the source-detector pairs. During calibrationof the source-detector pairs (described above), gain corrections aregenerated for the source-detector pairs and are stored in memory device205.

At 1820, control processor 200 of measurement module 120 fits (e.g., viaa sum of squares error calculation) the reflectance data points to thesimulated reflectance curves 600 to determine the particular reflectancedata curve that best fits (i.e., has the lowest fit error) thereflectance data points. According to one specific implementation, arelatively small set of simulated reflectance curves that are a “coarse”grid of the database of the simulated reflectance curves is selected andutilized for fitting step 1820. For example, given 39 scatteringcoefficient μ_(s)′ values and 150 absorption coefficient μ_(a) values, acoarse grid of simulated reflectance curves can be determined by controlprocessor 200 by taking every 5th scattering coefficient μ_(s)′ valueand every 8th absorption coefficients μ_(a) for a total of 40 simulatedreflectance curves in the coarse grid. It will be understood that theforegoing specific values are for an example embodiment and that coarsegrids of other sizes can be utilized by control processor 200. Theresult from fitting the reflectance data points to the coarse grid is acoordinate in the coarse grid (μ_(a), μ_(s)′)_(coarse) of the bestfitting simulated reflectance curve.

At 1825, the particular simulated reflectance curve from the coarse gridhaving the lowest fit error is utilized by control processor 200 todefine a “fine” grid of simulated reflectance curves where the simulatedreflectance curves in the fine grid are around the simulated reflectancecurve from the coarse grid having the lowest fit error.

That is, the fine grid is a defined size, with the lowest errorsimulated reflectance curve from the coarse grid defining the center ofthe fine grid. The fine grid may have the same number of simulatedreflectance curves as the coarse grid or it may have more or fewersimulated reflectance curves. The fine grid is substantially fine so asto provide a sufficient number of points to determine a peak surfacearray of nearby absorption coefficient μ_(a) values and scatteringcoefficient μ_(s)′ values, step 1830, in the fine grid. Specifically, athreshold can be set by control processor 200 utilizing the lowest errorvalue from the coarse grid plus a specified offset. The positions of thescattering coefficient μ_(s)′ and the absorption coefficient μ_(a) onthe fine grid that have errors below the threshold may all be identifiedfor use in determining the peak surface array for further determiningthe scattering coefficient μ_(s)′ and the absorption coefficient μ_(a)for the reflectance data. Specifically, an error fit is made for thepeak to determine the absorption coefficient μ_(a) and the scatteringcoefficient μ_(s)′ values at the peak. A weighted average (e.g., acentroid calculation) of the absorption coefficient μ_(a) and thescattering coefficient μ_(s)′ values at the peak can be utilized by thetissue oximetry device for the determination of the absorptioncoefficient μ_(a) and the scattering coefficient μ_(s)′ values for thereflectance data points for the tissue, step 1840.

Weights for the absorption coefficient μ_(a) and the scatteringcoefficient μ_(s)′ values for the weighted average can be determined bycontrol processor 200 as the threshold minus the fine grid error.Because points on the fine grid are selected with errors below thethreshold, this gives positive weights. The weighted calculation of theweighted average (e.g., centroid calculation) renders the predictedscattering coefficient μ_(s)′ and absorption coefficient μ_(a)(i.e.,(μ_(a), μ_(s)′) for the reflectance data points for the tissue. Othermethods can be utilized by the tissue oximetry device, such as fittingwith one or more of a variety of non-linear least squares to determinethe true minimum error peak for the scattering coefficient μ_(s)′.

According to one implementation, control processor 200 calculates thelog of the reflectance data points and the simulated reflectance curves,and divides each log by the square root of the source-detector distances(e.g., in centimeters). These log values divided by the square root ofthe of the source-detector distances can be utilized by controlprocessor 200 for the reflectance data points and the simulatedreflectance curves in the foregoing described steps (e.g., steps 1815,1820, 1825, and 1830) to improve the fit of the reflectance data pointsto the simulated reflectance curves.

According to another implementation, the offset is set essentially tozero, which effectively gives an offset of the difference between thecoarse grid minimum and the fine grid minimum. The method describedabove with respect to FIG. 18A relies on minimum fit error from thecoarse grid, so the true minimum error on the fine grid is typicallylower. Ideally, the threshold is determined from the lowest error on thefine grid, which would typically require additional computation by theprocessor.

The following is a further detailed description for finding theparticular simulated reflectance curve that best fits the reflectancedata points in the fine grid according to one implementation. FIG. 18Bis a high-level flow diagram of a method for finding the particularsimulated reflectance curve that best fits the reflectance data pointsin the fine grid according to one implementation. The high-level flowdiagram represents one example embodiment. Steps can be added to,removed from, or combined in the high-level flow diagram withoutdeviating from the scope of the embodiment.

Subsequent to determining the particular simulated reflectance curve(μ_(a) , μ_(s)′)_(coarse) from the coarse grid that best fits thereflectance data points at step 1825, control processor 200 computes anerror surface in a region about (μ_(a), μ_(s)′)_(coarse) in the fullsimulated reflectance curve database (i.e., 16 by 4 by 5850 (μ_(a),μ_(s)′) database) of simulated reflectance curves, step 1850. The errorsurface is denoted as: err(μ_(a), μ_(s)′). Thereafter, control processor200 locates the minimum error value in err(μ_(a), μ_(s)′), which isreferred to as err_(min), step 1855. Control processor 200 thengenerates a peak surface array from err(μ_(a), μ_(s)′) that is denotedby pksurf (μ_(a), μ_(s)′)=k+err_(min)−err(μ_(a), μ_(s)′) if the peaksurface is greater than zero, or pksurf (μ_(a),μ_(s)′)=k+err_(min)−err(μ_(a), μ_(s)′)=0 if the peak surface is lessthan or equal to zero, step 1860. In the expression k is chosen from apeak at the minimum point of err(μ_(a), μ_(s)′) with a width above zeroof approximately ten elements. The center-of-mass (i.e., the centroidcalculation) of the peak in pksurf (μ_(a), μ_(s)′) uses the heights ofthe points as weights, step 1865. The position of the center-of-mass isthe interpolated result for the absorption coefficient μ_(a) and thescattering coefficient μ_(s)′ for the reflectance data points for thetissue

The method described above with respect to FIGS. 18A and 18B fordetermining the absorption coefficient μ_(a) and the scatteringcoefficient μ_(s)′ for reflectance data points for tissue can berepeated for each of the wavelengths (e.g., 3 or 4 wavelengths)generated by each of light sources 150.

Oxygen Saturation Determination

According to a first implementation, control processor 200 determinesthe oxygen saturation for tissue that is probed by tissue oximetrydevice 100 by utilizing the absorption coefficients μ_(a) (e.g., 3 or 4absorption coefficients μ_(a)) that are determined (as described above)for the 3 or 4 wavelengths of light that are generated by each lightsource 120. According to a first implementation, a look-up table ofoxygen saturation values is generated for finding the best fit of theabsorption coefficients μ_(a) to the oxygen saturation. The look-uptable can be generated by assuming a range of likely total hemoglobin,melanin, and oxygen saturation values and calculating μ_(a) for each ofthese scenarios. Then, the absorption coefficient μ_(a) points areconverted to a unit vector by dividing by a norm of the unit vector toreduce systematic error and only depend on relative shape of curve. Thenthe unit vector is compared to the look-up table to find the best fit,which gives the oxygen saturation.

According to a second implementation, control processor 200 determinesthe oxygen saturation for the tissue by calculating the net analytesignal (NAS) of deoxygenated hemoglobin and oxygenated hemoglobin. TheNAS is defined as the portion of the spectrum that is orthogonal to theother spectral components in the system. For example, the NAS ofdeoxygenated hemoglobin is the portion of the spectrum that isorthogonal to oxygenated hemoglobin spectrum and melanin spectrum. Theconcentrations of deoxygenated and oxygenated hemoglobin can then becalculated by vector multiplying the respective NAS and dividing by anorm of the NAS squared. Oxygen saturation is then readily calculated asthe concentration of oxygenated hemoglobin divided by the sum ofoxygenated hemoglobin and deoxygenated hemoglobin. Anal. Chem.58:1167-1172 (1986) by Lorber is incorporated by reference herein andprovides a framework for a further detailed understanding of the secondimplementation for determining the oxygen saturation for the tissue.

According to one embodiment of tissue oximetry device 100, thereflectance data is generated by light detectors 170 at 30 Hertz, andoxygen saturation values are calculated at approximately 3 Hertz. Arunning average of determined oxygen saturation values (e.g., at leastthree oxygen saturation values) can be displayed on display 125, whichcan have an update rate of 1 Hertz.

Optical Properties

As described briefly above, each simulated reflectance curve 600 that isstored in memory device 205 represents unique optical properties oftissue. More specifically, the unique shapes of the simulatedreflectance curves, for a given wavelength, represent unique values ofthe optical properties of tissue, namely the scattering coefficient(μ_(s)), the absorption coefficient (μ_(a)), the anisotropy of thetissue (g), and index of refraction of the tissue.

The reflectance detected by light detectors 170 for relatively smallsource-to-detector distances is primarily dependent on the reducedscattering coefficient, μ_(s)′. The reduced scattering coefficient is a“lumped” property that incorporates the scattering coefficient μ_(s) andthe anisotropy g of the tissue where μ_(s)′=μ_(s)(1-g), and is used todescribe the diffusion of photons in a random walk of many steps of sizeof 1/μ_(s)′ where each step involves isotropic scattering. Such adescription is equivalent to a description of photon movement using manysmall steps 1/μ_(s) which each involve only a partial deflection angleif there are many scattering events before an absorption event, i.e.,μ_(a)«μ_(s)′.

In contrast, the reflectance that is detected by light detectors 170 forrelatively large source-detector distances is primarily dependent on theeffective absorption coefficient μ_(eff), which is defined as √{squareroot over (3μ_(a)(μ_(a)+μ_(s)′))}, which is a function of both μ_(a) andμ_(s)′.

Thus, by measuring reflectance at relatively small source-detectordistances (e.g., the distance between light source 150 a and lightdetector 170 e and the distance between light source 120 b and lightdetector 170 a) and relatively large source-detector distances (e.g.,the distance between light source 150 a and detector 170 a and thedistance between light source 120 b and detector 170 e), both μ_(a) andμ_(s)′ can be independently determined from one another. The opticalproperties of the tissue can in turn provide sufficient information forthe calculation of oxygenated hemoglobin and deoxygenated hemoglobinconcentrations and hence the oxygen saturation of the tissue.

Iterative Fit for Data Collection Optimization.

FIG. 19 is a high-level flow diagram of another method for determiningthe optical properties of tissue by tissue oximetry device 100. Thehigh-level flow diagram represents one example embodiment. Steps can beadded to, removed from, or combined in the high-level flow diagramwithout deviating from the scope of the embodiment.

At 1900, tissue oximetry device 100 emits light from one of the lightsources, such as light source 150 a into tissue. After the emitted lightreflects from the tissue, light detectors 170 detect the light, step1905, and generate reflectance data for the tissue, step 1910. Steps1900, 1905, and 1910 can be repeated for multiple wavelengths of lightand for one or more other light sources, such as light source 150 b. At1915, control processor 200 fits the reflectance data to simulatedreflectance curves 600 and determines the simulated reflectance curve towhich the reflectance data has the best fit. Thereafter, controlprocessor 200 determines the optical properties (e.g., μ_(a), andμ_(s)′) for the tissue based on the optical properties of the simulatedreflectance curve that best fits the reflectance data, step 1920.

At 1925 control processor 200 determines the mean free path of the lightin the tissue from the optical properties (e.g., mfp=1/(μ_(a)+μ_(s)′)determined at step 1920. Specifically, the mean free path can bedetermined from the optical properties obtained from a cumulativereflectance curve that includes the reflectance data for all of thesource-detector pairs (e.g., pair 1: light source 150 a-detector 170 e;pair 2: light source 150 a-detector 170 f; pair 3: light source 150a-detector 170 g; pair 4: light source 150 a-detector 170 h; pair 5:light source 150 a-detector 170 a; pair 6: light source 150 a-detector170 b; pair 7: light source 150 a-detector 170 c; pair 8: light source150 a-detector 170 d; . . . pair 9: light source 150 b-detector 170 e,pair 10: light source 150 b-detector 170 f . . . and others.).

At 1930, control processor 200 determines whether the mean free pathcalculated for a given region of the tissue is longer than two times theshortest source-to-detector distance (e.g., the distance between lightsource 150 a and detector 170 e, and the distance between light source150 b and detector 170 a). If the mean free path is longer than twotimes the shortest source-to-detector distance, then the collectedreflectance data is re-fitted to the simulated reflectance curves (i.e.,reanalyzed) without utilizing the reflectance data collected from thedetectors for the source-to-detector pairs (e.g., pair 1: light source150 a-detector 170 e and pair 9 light source 150 b-detector 170 a)having the shortest source-to-detector distance. For example, steps1915-1930 are repeated without use of the reflectance data from detector170 e with light source 150 a acting as the source for detector 170 e,and without use of the reflectance data from detector 170 a with lightsource 150 b acting as the source for detector 170 a. The process ofcalculating the mean free path and discarding the reflectance data forone or more source-detector pairs can be repeated until nosource-detector pairs that contribute reflectance data to the fit have asource-to-detector distance shorter than one half of the calculated meanfree path. Thereafter, oxygen saturation is determined from the bestfitting simulated reflectance curve and reported by tissue oximetrydevice 110, such as on display 125, step 1935.

Light that is emitted from one of the light sources 150 into tissue andthat travels less than half of the mean free path is substantiallynondiffusely reflected. The re-emission distance for this light isstrongly dependent on the tissue phase function and the local tissuecomposition. Therefore, using the reflectance data for this light tendsto result in a less accurate determination of the optical properties andtissue properties as compared with the reflectance data for light thathas undergone multiple scattering events.

Data Weighting

Light detectors 170 that are positioned at increasing distances fromlight sources 150 receive decreasing amounts of reflectance from tissue.Therefore, the reflectance data generated by light detectors 170 havingrelatively short source-to-detector distances (e.g., source-to-detectordistances less than or equal to the average distance between the lightsources and the light detectors) tends to exhibit intrinsically lowernoise compared to reflectance data generated by detectors havingrelatively long source-to-detector distances (e.g., source-to-detectordistances greater than the average distance).

Fit algorithms may therefore preferentially fit the simulatedreflectance curves to the reflectance data that is generated by lightdetectors 170 having relatively short source-to-detectors distances(e.g., source-to-detector distances less than or equal to the averagedistance between the light sources and the light detectors) more tightlythan reflectance data that is generated by light detectors havingrelatively long source-to-detector distances (e.g., source-to-detectordistances greater than the average distance). For relatively accuratedetermination of the optical properties from the reflectance data, thisdistance-proportional skew can be undesirable and can be corrected byweighting the reflectance data as described immediately below.

FIG. 20 is a high-level flow diagram of a method for weightingreflectance data generated by select light detectors 170. The high-levelflow diagram represents one example embodiment. Steps can be added to,removed from, or combined in the high-level flow diagram withoutdeviating from the scope of the embodiment.

At 2000, tissue oximetry device 100 emits light from one of the lightsources, such as light source 150 a into tissue. After the emitted lightreflects from the tissue, light detectors 170 detect the light, step2005, and generate reflectance data for the tissue, step 2010. Steps2000, 2005, and 2010 can be repeated for multiple wavelengths of lightand for one or more other light sources, such as light source 150 b. At2015, control processor 200 fits a first portion of the reflectance datato the simulated reflectance curves.

The first portion of the reflectance data is generated by a firstportion of detectors that are less than a threshold distance from thelight source. The threshold distance can be the average distances (e.g.,approximate mid-range distance) between the light sources and the lightdetectors. At 2020, reflectance data for a second portion of thereflectance data is fitted to the simulated reflectance curves. Thesecond portion of reflectance data is generated by the first portion ofthe light detectors and another light detector that is at the nextlargest source-to-detector distance from the light source compared tothe threshold distance. For example, if the first portion of lightdetectors includes light detectors 170 c, 170 d, 170 e, and 170 f, thenthe light detector that is at the next largest source-to-detectordistance is detector 170 g (e.g., closer to light source 150 a thandetector 170 c, see FIGS. 9A and 9B).

At 2025, the fit generated at step 2015 is compared to the fit generatedat step 2020 to determine whether the fit generated at step 2020 isbetter than the fit generated at 2015. As will be understood by those ofskill in the art, a “closeness” of a fit of data to a curve isquantifiable based on a variety of parameters, and the closeness of fitsare directly comparable to determine the data having a closer fit(closer fit) to a curve. As will be further understood, a closer fit issometimes also referred to as a better fit or a tighter fit.

If the fit generated at step 2020 is better than the fit generated atstep 2015, then steps 2020 and 2025 are repeated with reflectance datathat is generated by light detectors that include an additional lightdetector (according to the example being considered, light detector 170c) that is positioned at a next increased source-to-detector distancefrom the source. Alternatively, if the fit generated at step 2020 is notbetter than the fit generated at step 2015, then the reflectance datafor light detectors 170 that are positioned at source-to-detectordistances that are greater than the threshold distance are not used inthe fit. Thereafter, control processor 200 uses the fit generated at2015 or step 2020 (if better than the fit determined at step 2015) todetermine the optical properties and the oxygen saturation of thetissue, step 2030. Thereafter, oxygen saturation is reported by tissueoximetry device 110, such as on display 125, step 2035.

According to an alternative embodiment, if the fit generated at step2020 is not better than the fit generated at step 2015, then thereflectance data are weighted by a weighting factor for light detectorsthat have source-to-detector distances that are greater than thethreshold distance so that this weighted reflectance data has adecreased influence on the fit. Reflectance data that is not used in afit can be considered as having a zero weight and can be associated withreflectance from tissue below the tissue layer of interest. Reflectancefrom tissue below the tissue layer of interest is said to exhibit acharacteristic kink in the reflectance curve that indicates thisparticular reflectance.

It is noted that curve-fitting algorithms that fit the reflectance datato the simulated reflectance curves may take into account the amount ofuncertainty of the reflectance data as well as the absolute location ofthe reflectance data. Uncertainty in the reflectance data corresponds tothe amount of noise from the generation of the reflectance data by oneof the light detectors, and the amount of noise can scale as the squareroot of the magnitude of the reflectance data.

According to a further embodiment, control processor 200 iterativelyweights the reflectance data based on the amount of noise associatedwith the measurements of the reflectance data. Specifically, thereflectance data generated by light detectors having relatively largesource-to-detector distances generally have lower signal-to-noise ratiocompared to the reflectance data generated by light detector havingrelatively short source-to-detector distances. Reducing the weighting ofthe reflectance data generated by light detectors having relativelylarge source-to-detector distances allows for this data to influence tothe fit less than other reflectance data.

Calibration

According to one embodiment, tissue oximetry device 100 is calibratedutilizing a number (e.g., three to thirty) of tissue phantoms that haveknown optical properties. Tissue oximetry device 100 can be used toprobe the tissue phantoms and collect reflectance data for the tissuephantoms. The reflectance data for each tissue phantom can be fitted tosimulated reflectance curves 600. The reflectance data generated foreach tissue phantom should fit a simulated reflectance curve, which hasthe same optical properties as the tissue phantom. If the reflectancedata does not fit well to the simulated curve that matches the opticalproperties of the tissue phantom, then a calibration function can begenerated by control processor 200 to improve the fit. One or more ofthe calibration functions or an average of the calibration functions canbe stored in memory device 205. The one or more calibration functionscan be applied to reflectance data generated for real tissue that isprobed by tissue oximetry device 100 so that the reflectance data forthe real tissue will fit to one of the simulated reflectance curves thathas optical properties that are a substantially accurate match to theoptical properties of the real tissue. Thereafter, the opticalproperties for the matched simulated reflectance curve can be used tocalculate and report the oxygenation saturation of the real tissue.

Pressure Sensor

As described briefly above, probe tip 300 may include at least onepressure sensor 175. Pressure sensor 175 can be located on a face ofprobe tip 300, between various components of sensor head 250 (e.g.,between probe tip 300 and disk shaped end 105 d of housing 105), betweenvarious components of probe tip 300, or the like. Pressure sensor 175 isconfigured to detect the pressure at which probe tip 300 is pressedagainst tissue that is being probed. Pressure sensor 175 may detectpressures from about 0 millimeters of mercury to about 100 millimetersof mercury. In other implementations, the pressure sensor can beomitted.

Pressure sensor 175 can be a force sensing resistor (FSR), apiezoelectric pressure sensor, a capacitive pressure sensor, aninductive pressure sensor, a load cell, or the like, or may include oneor more of these sensors in combination, such as an FSR and a load cell.According to one specific embodiment, pressure sensor 175 is an FSRproduced by Interlink Electronics and is sold under the brand nameStandard 400 FSR. FIG. 21 shows back and front views of an FSR that canbe used with tissue oximetry device 100. The FSR can be produced byInterlink Electronics and sold under the brand name Standard 400 FSR.The FSR includes a pressure sensing regions and a set of traces in a PCBfor transmitting electrical signal from the FSR to acquisition module115, measurement module 120, or both.

In one implementation, a non-zero preload force is applied to pressuresensor 175 by components of probe tip 130, sensor head 250, housing 105,or a combination of these. Further, acquisition module 115, measurementmodule 120, or both may perform a tare operation on pressure sensor 175after tissue oximetry device 100 is turned on. Taring pressure sensor175 after tissue oximetry device 100 is turned on corrects for pressurechanges on the pressure sensor that may have occurred during assembly,shipping, storage, or other causes.

FIG. 22A is a simplified image of display 125, which can be configuredto display a pressure indicator 177 that indicates the amount ofpressure sensed by pressure sensor 175. Pressure indicator 177 mayinclude a numerical indicator (now shown), a graphical indictor (shownin FIG. 22A), or both for indicating pressure detected by pressuresensor 175. The numerical indicator may display the detected pressure inmillimeters of mercury, pound per square inch, grams per squarecentimeter, or other units. Alternatively, the numerical indicator maydisplay the force applied by tissue oximetry device 100 on tissue beingprobed.

In one embodiment, the graphical indicator is a one-dimensional graph,such as a one-dimensional bar graph, a two-dimensional graph, or thelike that graphically indicates the detected pressure. For example, ifthe graphical indicator is a one-dimensional bar graph as shown in FIG.22A, the percentage of the bar graph filled in (e.g., with a givencolor) indicates the detected pressure.

The graphical indicator may include additional graphical marks (e.g.,arrows shown in FIG. 22A) to indicate that the detected pressure is inan optimal pressure range. For example, the portion of the bar graphbetween the arrows may indicate the optimal pressure range. Optimalpressure ranges are described in further detail below.

Pressure indicator 177 or a portion thereof can be displayed in a uniquemanner if the detected pressure is in the optimal pressure range. Forexample, the numerical indicator and/or the graphical indicator can bedisplayed in a first color (e.g., red) if the detected pressure is notin the optimal pressure range, and can be displayed in a second color(e.g., green) if the detected pressure is in the optimal pressure range.According to another example, the portion of the one-dimensional bargraph for the optimal pressure range and the graphical marks (e.g.,arrows) that indicate the optimal pressure range can be displayed in thesecond color (e.g., green) to indicate that optimal pressure isdetected, and other portions of the one-dimensional bar graph outside ofthe graphical marks can be displayed in the first color (e.g., red) toindicate that the optimal pressure is not detected.

While display 125 is described herein as being configured to display anindicator 178 for oxygen saturation and an indicator 177 for appliedpressure, other display devices can be configured to display theseindicators, such as the display of a detached base unit or an externaldisplay that is configured to wire or wirelessly communicate with tissueoximetry device 100.

Turning now to the optimal pressure range, the optimal pressure range isa range in which valid oxygen saturation measurements can be made bytissue oximetry device 100. Pressures applied within the optimalpressure range are sufficiently large enough to seal probe tip 300against tissue being probed so that light from ambient sources does notleak into light detectors 170. Further, pressures applied within theoptimal pressure range are also sufficiently small so that blood withintissue being probed is not pressed from the tissue or inhibited fromflowing into the tissue so that oxygen saturation measurements are notskewed. More specifically, applied pressures above an upper limit of theoptimal pressure range may indicate that the pressure of probe tip 300on tissue is relatively high and is pressing blood from the tissue suchthat an oxygen saturation measurement will be adversely affected bythese pressures.

The optimal range of applied pressure for probe tip 300 on tissue can bedifferent for different patients. For example, the optimal range ofapplied pressure can be lower for a patient with diabetes as compared toa normally healthy patient without diabetes. For example, the optimalpressure range for a normally healthy patient can be from about 10millimeters of mercury to about 30 millimeters of mercury, whereas theoptimal pressure range for a patient with diabetes can be from about 5millimeters of mercury to about 25 millimeters of mercury.

One or more optimal pressure ranges can be empirically predetermined andinformation for the one or more optimal pressure ranges can be stored inmemory device 205. Tissue oximetry device 100 may include one or more ofa variety of devices that can be used to select the information for oneof the optimal pressure ranges stored in memory device 205. For example,one or more of the input controllers 130 can be configured for switchingbetween the various optimal pressure ranges. Alternatively, display 125can be a touch screen and can be configured to display one or moredisplay buttons (e.g., a specific example of one of the inputcontrollers 130) where the display buttons can be touched and/or pressedfor selecting one of the optimal pressure ranges. Display 125 may alsodisplay an indicator for the particular optimal pressure range selected.The indicator for the particular optimal pressure range selected mayinclude a “condition” indicator that indicates the condition (i.e.,normal, diabetic, or other conditions) that is associated with theparticular optimal pressure range selected.

Display 125 may also display a total time 176 of use of tissue oximetrydevice 100. The use time can be tracked by measurement module 120 fordisplay on display 125. Display 125 can also display a low batteryindicator 179 if the battery power is low. In another alternative,display 125 can display a power meter (not shown) that indicates thecharge remaining in batteries 220.

FIG. 23 is a high-level flow diagram of a method for measuring thepressure of probe tip 300 against tissue being probed and for indicatingwhether a tissue oximetry measurement of the tissue oximetry device 100is valid based on the pressure. The high-level flow diagram representsone example embodiment. Steps can be added to, removed from, or combinedin the high-level flow diagram without deviating from the scope of theembodiment.

At 2300, probe tip 300 contacts the tissue. Light (e.g., near infraredlight) is emitted from one or more of the light sources 150, step 2305,into the tissue and at least some of the light is reflected back by thetissue. Each light detector 170 receives a portion of the lightreflected from the tissue, step 2310, and each light detector generatesreflectance data (i.e., a response) for the portion of reflected lightreceived, step 2315. At 2320, control processor 200 determines an oxygensaturation value for the tissue based on the reflectance data. At 2325,pressure sensor 175 measures the pressure (or force) of probe tip 300 onthe tissue. At 2330, display 125 displays pressure indicator 177 anddisplays an indicator for the oxygen saturation. Pressure indicator 177indicates whether the oxygen saturation measured is valid or invalidbased on the pressure. For example, pressure indicator 177 can bedisplayed in the second color (e.g., green) if the pressure is within anoptimal pressure range for which valid oxygen saturation measurementscan be made, and in the first color (e.g., red) if the pressure is notwithin the optimal pressure range. While the utilization of color isdescribed for indicating whether the oxygen saturation measurement isvalid, other indicators can be used for such indication, such asflashing text or graphics, changed fonts, use of dashed lines forindicator 178 (see FIG. 22B) for the oxygen saturation, or otherindications. The mark (e.g., dashed lines) for indicating that a validoxygen saturation cannot be made, can be displayed for a variety ofconditions described herein.

The steps of the pressure-sensing method can be substantiallycontinuously repeated so that a user using tissue oximetry device 100receives updated feedback (i.e., pressure indicator 177) as the userincreases or decreases the pressure applied to the tissue so that apressure within the optimal pressure range is applied and so that validtissue oximetry measurements are made.

Tissue Marking

According to one embodiment, tissue oximetry device 100 includes atissue marker that is configured to mark tissue. FIG. 24 shows anembodiment of probe tip 300 where the probe tip 300 includes at least adispenser portion 700 of the tissue marker. The dispenser portion of thetissue marker can be located at a variety positions on the face of probetip 300. According to one specific embodiment, the dispenser portion islocated between light sources 150 a and 150 b, and can be located at theapproximate center of the circular arrangement of detectors 170. Withthe dispenser at the approximate center of light sources 150 anddetectors 170, a mark made by the dispenser will be substantially at acenter of the local tissue region that has been probed by tissueoximetry device 100. With the mark at the center of the probed tissueregion, the mark is not displaced from the location on the local tissueregion probed.

According to one implementation, the tissue marker includes one or moredispensers that can be located at different positions of probe tip 200.For example, two dispensers can be located “outside” of light sources150 and light detectors 170. That is, the dispensers can be located atthe ends of radii that are longer than the radii of the locations oflight sources 150 and detectors 170. Further, the dispensers may lie ona line that passes through the center of the circle of the circulararrangement of light detectors 170. With the dispensers located alongsuch a line, marks made by these dispensers allow a user to readilyidentify the region between the marks as the local tissue region thathas been probed by tissue oximetry device 100.

While the dispenser is shown in FIG. 24 as being relatively localizeddevices (e.g., pen, pens, inker, inkers, and the like) that can beconfigured to mark tissue with relatively small marks (e.g., dots), adispenser can be an extended device configured to make an extended mark,such as a line. For example, a dispenser can be an extended deviceconfigured to mark tissue with a circle or other closed shape, or maymark tissue with an open shape, such as a u-shape, a v-shape, or others.

The dispenser can be fixed within probe tip 300 or can be configured tobe lowered when tissue is marked. Various mechanical orelectromechanical devices can be utilized by probe tip 300 for loweringthe dispenser. Such mechanical and electro-mechanical devices are wellunderstood by those of skill in the art and are not described in detailherein.

The tissue marker may mark tissue with a variety of inks having avariety of colors, such as gentian violet, which is the tissue markingink approved by the FDA. One or more of the ink colors utilized bytissue oximetry device 100 may indicate one or more oxygen saturationranges. For example, the tissue marker can be configured to: (i) marktissue with a first color of ink if the tissue's oxygen saturation is ator below a first threshold, (ii) mark the tissue with a second color ofink if the tissue's oxygen saturation is above the first threshold andat or below a second threshold, and (iii) mark the tissue with a thirdcolor of ink if the tissue's oxygen saturation is above the secondthreshold. The foregoing example describes the use of three colors ofink for marking tissue for visually identifying three ranges of oxygensaturation, however more or fewer colors can be utilized by the tissuemarker for identifying more or fewer oxygen saturation ranges.

Control processor 200 may determine the oxygen saturation of a localtissue region based on an analysis of the reflection data as describedabove, and may control the tissue marker to mark the local tissue regionwith a select color of ink that identifies the range that the oxygensaturation is within. The tissue marker may include a variety of devicesthat provide marking material having one or more colors, such as inkreservoirs, pens, or the like. U.S. patent application 12,178,359, filedJul. 23, 2008, of Heaton, titled “Oximeter with Marking Feature,” whichis incorporated by reference, describes a variety of devices that areconfigured for marking tissue with one or more colors of markingmaterial.

A reservoir of the tissue marker can be connected to the dispenser, suchas through tubing or channels, and may contain ink or other fluids(e.g., ink) dispensed through the dispenser. Ink can be moved from thereservoir to and through the dispenser and deposited on skin throughpressure or low-frequency sound (such using a piezoelectric transducer).The reservoir can be contained within housing 105. For the disposableprobe, the reservoir may not be refillable.

According to one alternative, the tissue marker, under control ofprocessor 116, marks tissue for one or more oxygen saturation ranges,but does not mark the tissue for one or more other oxygen saturationregions. For example, the tissue marker can mark a local tissue regionif the oxygen saturation of the local tissue region is at or below athreshold level, or alternatively does not mark the local tissue regionif the oxygen saturation level is above the threshold level. Markingsthat are made on tissue according to the above method allow a user torelatively quickly identify tissue that can have a low chance ofviability if the threshold level is relatively low. Alternatively, thetissue marker can mark a local tissue region if the oxygen saturation ofthe local tissue region is at or above a threshold level, and might notmark the local tissue region if the oxygen saturation level is below thethreshold level. Marks made from this method allow a user to relativelyquickly identify tissue that can have a relatively high chance ofviability if the threshold level is relatively high.

Information for the foregoing described threshold levels (i.e., ranges)can be stored in memory device 205 and accessed by control processor 200for use. The threshold levels can be stored in memory device 205 duringmanufacture of tissue oximetry device 100, or can be stored in thememory thereafter. For example, tissue oximetry device 100 can beconfigured to receive a user input for one or more user definedthreshold levels and store information for these threshold levels inmemory device 205. One or more input controllers 130 (or the like) canbe configured to receive a user input for a user defined threshold leveland for storing the user defined threshold level in memory device 205.

FIG. 25 is a high-level flow diagram of a method for marking tissue toindicate ranges of oxygen saturation of the tissue. The high-level flowdiagram represents one example embodiment. Steps can be added to,removed from, or combined in the high-level flow diagram withoutdeviating from the scope of the embodiment.

At 2500, probe tip 300 contacts the tissue. Light (e.g., near infraredlight) is emitted from one or more of the light sources 150, step 2505,into the tissue and at least some of the light is reflected back by thetissue. Each light detector 170 receives a portion of the lightreflected from the tissue, step 2510, and each light detector generatesreflectance data (i.e., a response) for the portion of reflected lightreceived, step 2515. At 2520, control processor 200 determines an oxygensaturation value for the tissue based on the reflectance data asdescribed above.

At 2525, control processor 200 determines a range of oxygen saturationfrom a plurality of ranges of oxygen saturation in which the oxygensaturation lies. At 2530, control processor 200 controls the tissuemarker to mark the tissue with ink based on a range in which the oxygensaturation is in. For example, the control processor can be configuredto control the dispenser to mark the tissue with ink if the oxygensaturation is in a first range of oxygen saturation, but not mark thetissue if the oxygen saturation in a second range of oxygen saturationwhere the first range and second range are different, such as notoverlapping ranges. While the foregoing example embodiment, discussesthe utilization of two ranges of oxygen saturation by the tissueoximetry device, the tissue oximetry device may utilize more than tworanges of oxygen saturation for determining whether to mark the tissuewith ink.

According to one embodiment, control processor 200 may control thedispenser to mark the tissue with a specific color of ink based on therange of oxygen saturation that the oxygen saturation is in. Theparticular color of ink allows a user to relatively quickly determinethe ranges of oxygen saturation for the tissue without the need forre-probing the tissue or looking at a chart of the tissue that includesoxygen saturation values and matching the chart to the tissue.

Tissue oximetry device 100 can be configured to allow a user to manuallycontrol the tissue oximetry device to mark tissue, allow controlprocessor 200 to control marking the tissue, or both. Tissue oximetrydevice 100 can be switched between the processor controlled method ofmarking tissue and the manually controlled method (e.g., by activatingone of the input controllers 130) of marking tissue.

Laparoscopy

In one application of tissue oximetry probe 100, the tissue oximetryprobe can be used by a physician for a laparoscope procedure to measurethe oxygen saturation of tissues within a patient. In a laparoscopeprocedure, probe tip 300 of tissue oximetry probe 100 may be insertedinto a relatively small incision (e.g., about 0.5 centimeters to about 2centimeters) in a patient (e.g., in the patient's abdomen or pelvis) andpressed into contact with tissue for which an oxygen saturationmeasurement is to be made. In some use cases, probe head 250, tipportion 105 c of housing 105, or both may also be inserted into theincision if the probe tip is to be moved further into the incision.

In this application, tissue oximetry probe 100 can be used incombination with a lighting system and a camera system that can beconfigured to be inserted in a different incision from the incision usedfor the tissue oximetry probe or the same incision. For example, probetip 300 can be coupled to the lighting system and the camera system forinsertion into a single incision. Probe tip 300 can be configured to beplaced in or on a laparoscope tube that houses the lighting system andthe camera system. In this embodiment, probe tip 300 may be coupled totissue oximetry device 100 by a variety of devices. For example, probetip 300 may be optically coupled by extended waveguides that are in-turnoptically coupled to light sources, light detector, or both in housing105. According to another example, probe tip 300 may be electricallycoupled to acquisition module 115 by extended electrical wires, traces,or the like. The camera system might include a telescopic rod lenssystem that is connected to a video camera that is located outside ofthe patient's body, or might include a digital laparoscope where aminiature digital video camera is placed at the end of the digitallaparoscope that is positioned in the patient during the laparoscopeprocedure.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

The invention claimed is:
 1. A method comprising: enclosing in a housinga first printed circuit board comprising a processor and a memory,wherein the memory is coupled to the processor; providing a display,coupled to the processor and the housing, wherein the display is visiblefrom an exterior side of the housing, wherein a shape of the housingcomprises: a back surface of the housing which during use, rests betweena thumb and forefinger of the hand, a probe tip comprising a relativelyplanar surface comprising sensor openings, wherein the relatively planarsurface is angled at a nonzero angle relative to the back surface, a topsurface of the housing comprising the display, wherein the top surfaceis angled at a nonzero angle relative to the back surface, and a tubularhand grip region, comprising the back surface, coupled between the topsurface and the probe tip; and forming a structure of the housing toretain the probe tip, wherein the probe tip is coupled to an exteriorside of the enclosure.
 2. The method of claim 1 wherein the probe tipcomprises at least a first sensor opening, a second sensor opening, athird sensor opening, and a fourth sensor opening, a first distance isbetween the first and second sensor openings, a second distance isbetween the first and third sensor openings, and a third distance isbetween the first sensor opening and the fourth sensor opening, and thefirst distance is different from the second distance, and the thirddistance is greater than the first distance and the second distance. 3.The method of claim 1 comprising: providing a first light source for thefirst sensor opening, wherein the first sensor opening is coupled via anoptical fiber to the first light source; providing light detectors forthe second and the third sensor openings, wherein the second and thethird sensor openings are coupled via channels to the light detectors,and the optical fiber has a length that is longer than each of thechannels; and providing a second light source for the fourth sensoropening, wherein the first sensor opening is coupled via an opticalfiber to the second light source.
 4. The method of claim 2 comprising:providing a first light source for the first sensor opening, wherein thefirst sensor opening is coupled via an optical fiber to the first lightsource; providing light detectors for the second and the third sensoropenings, wherein the second and the third sensor openings are coupledvia channels to the light detectors, and the optical fiber has a lengththat is longer than each of the channels; and providing a second lightsource for the fourth sensor opening, wherein the first sensor openingis coupled via an optical fiber to the second light source.
 5. Themethod of claim 2 comprising: configuring the probe tip to receive firstdata associated with the first and the second sensor openings;configuring the probe tip to receive second data associated with thefirst and the third sensor openings; and configuring the processor toperform spatially-resolved spectroscopy using the first and the seconddata to determine an oxygen saturation value.
 6. The method of claim 2wherein a fourth distance is between the second and fourth sensoropenings, and a fifth distance is between the third and fourth sensoropenings, the fourth distance is different from the first distance, andthe fifth distance is different from the second distance.
 7. The methodof claim 5 comprising: configuring the probe tip to receive third dataassociated with the second sensor and fourth sensor openings;configuring the probe tip to receive fourth data associated with thethird sensor and fourth sensor openings, wherein configuring theprocessor to perform spatially-resolved spectroscopy also uses the thirdand fourth data in determining the oxygen saturation value.
 8. Themethod of claim 1 wherein a shape of the housing comprises a frontsurface, and the front surface is coupled between the top surface andtubular hand grip region.
 9. The method of claim 8 comprising: forming abutton on the front surface.
 10. An oximeter device comprising: ahousing comprising: a processor, contained within the housing; a memory,contained within the housing, wherein the memory is coupled to theprocessor; a display, coupled to the processor, wherein the display isvisible from an exterior of the housing; and a sensor module, coupled tothe processor, wherein the sensor module comprises a probe face that isretained by a tip portion of the housing at a relatively fixed positionwith respect to the housing and that is placed against and faces tissueto be measured, and the probe face comprises: a first source structureand a second source structure, formed on the probe face; a firstdetector structure, formed on the probe face, wherein a first distanceis from the first detector structure to the first source structure, asecond distance is from the first detector structure to the secondsource structure, and the first distance is greater than the seconddistance; a second detector structure, formed on the probe face, whereina third distance is from the second detector structure to the firstsource structure, a fourth distance is from the second detectorstructure to the second source structure, and the fourth distance isgreater than the third distance, and the first distance is the same asthe fourth distance, and the second distance is the same as the thirddistance; a third detector structure, formed on the probe face, whereina fifth distance is from the third detector structure to the firstsource structure, a sixth distance is from the third detector structureto the second source structure, the fifth distance is different from thefirst distance and the second distance, and the sixth distance isdifferent from the first distance and the second distance; and a fourthdetector structure, formed on the probe face, wherein a seventh distanceis from the fourth detector structure to the first source structure, aneighth distance is from the fourth detector structure to the secondsource structure, the seventh distance is different from the first,second, and fifth distances, and the eighth distance is different fromthe first, second, and sixth distances, and the first distance isgreater than the second, third, fifth, sixth, seventh, and eighthdistances, and the second distance is less than the fifth, sixth,seventh, and eight distances.
 11. The device of claim 10 wherein inoperation, the processor collects first information from the firstdetector structure in response to radiation emitted from the firstsource structure.
 12. The device of claim 11 wherein the firstinformation is reflective of the tissue to be measured at a first depthbelow a surface of the tissue
 13. The device of claim 11 wherein inoperation, the processor collects second information from the seconddetector structure in response to radiation emitted from the firstsource structure.
 14. The device of claim 13 wherein the secondinformation is reflective of the tissue to be measured at a second depthbelow the surface of the tissue.
 15. The device of claim 13 wherein thesecond depth is less than the first depth.
 16. The device of claim 15wherein the tissue to be measured at the first depth is above asubcutaneous fat layer and muscle layer that are below the surface ofthe tissue.
 17. The device of claim 10 wherein the sensor modulecomprises: a first source diode and a second source diode; a firstoptical fiber, coupled between the first source structure and the firstsource diode; and a second optical fiber, coupled between the secondsource structure and the second source diode.
 18. The device of claim 10wherein the first detector structure comprises a first photodetectorpositioned on the probe face, the second detector structure comprises asecond photodetector positioned on the probe face, the third detectorstructure comprises a third photodetector positioned on the probe face,and the fourth detector structure comprises a fourth photodetectorpositioned on the probe face.
 19. The device of claim 10 wherein thesensor module comprises: a first photodetector, a second photodetector,a third photodetector, and a fourth photodetector; a first waveguide,coupled between the first detector structure and the firstphotodetector; a second waveguide, coupled between the second detectorstructure and the second photodetector; a third waveguide, coupledbetween the third detector structure and the third photodetector; and afourth waveguide, coupled between the fourth detector structure and thefourth photodetector.
 20. The device of claim 10 wherein the sensormodule comprises a temperature sensing unit configured to generatetemperature information that represents the temperature of the firstsource structure.
 21. The device of claim 20 wherein the processor isconfigured to adjust a duty cycle of an oscillating control signalsupplied to the first source structure to adjust the luminositygenerated by the first source structure based on the temperatureinformation if the temperature of the first source structure changes.